Add DB decode annotations and preserved declaration metadata

AGENTS.md

@@ -13,6 +13,7 @@
 - Prefer defining Lyng entities (enums/classes/type shapes) in `.lyng` files; only define them in Kotlin when there is Kotlin/platform-specific implementation detail that cannot be expressed in Lyng.
 - Avoid hardcoding Lyng API documentation in Kotlin registrars when it can be declared in `.lyng`; Kotlin-side docs should be fallback/bridge only.
 - For mixed pluggable modules (Lyng + Kotlin), embed module `.lyng` sources as generated Kotlin string literals, evaluate them into module scope during registration, then attach Kotlin implementations/bindings.
+- When a change adds or changes Lyng-visible runtime/module behavior, update the corresponding `.lyng` declaration in the same change, including declaration-level docs/comments for new API surface.
 
 ## Kotlin/Wasm generation guardrails
 - Avoid creating suspend lambdas for compiler runtime statements. Prefer explicit `object : Statement()` with `override suspend fun execute(...)`.

docs/lyng.io.db.md

@@ -207,14 +207,27 @@ assertThrows(RollbackException) {
 - `isEmpty()` — fast emptiness check where possible.
 - `iterator()` — normal row iteration while the transaction is active.
 - `toList()` — materialize detached `SqlRow` snapshots that may be used after the transaction ends.
+- `decodeAs<T>()` — transaction-scoped iterable view that decodes each row into `T`.
 
 ##### `SqlRow`
 
 - `row[index]` — zero-based positional access.
 - `row["columnName"]` — case-insensitive lookup by output column label.
+- `row.decodeAs<T>()` — decode one row into a typed Lyng value.
 
 Name-based access fails with `SqlUsageException` if the name is missing or ambiguous.
 
+##### `DbFieldAdapter`
+
+Custom DB field projection hook used by `@DbDecodeWith(...)`.
+
+- `decode(rawValue, column, row, targetType)` — adapt one raw DB field value to a Lyng value for the requested target type.
+- `encode(value, targetType)` — future symmetric hook for SQL parameter encoding.
+
+Use `@DbDecodeWith(adapter)` on class constructor parameters and class-body fields/properties that participate in `decodeAs<T>()`.
+
+Annotation arguments are evaluated once when the declaration is created, and the resulting adapter instance is retained in declaration metadata.
+
 ##### `ExecutionResult`
 
 - `affectedRowsCount`
@@ -249,6 +262,22 @@ Portable result metadata categories:
 - `DateTime`
 - `Instant`
 
+Typed row decode rules:
+
+- object/class targets map constructor parameters by column label, case-insensitively
+- remaining matching serializable mutable fields are assigned after constructor call
+- `@DbDecodeWith(adapter)` on a constructor parameter or class-body field/property takes precedence over built-in JSON/Lynon decoding
+- `@DbDecodeWith(adapter)` must receive exactly one adapter instance implementing `DbFieldAdapter`
+- adapter output must match the target member type or decoding fails with `SqlUsageException`
+- missing required non-null constructor fields fail
+- defaulted or nullable constructor fields may be omitted from the result
+- extra result columns currently fail in strict mode
+- if a row has exactly one column, that value may be decoded directly as the requested target type
+- JSON-like native column types (`json`, `jsonb`) are decoded through typed canonical `Json` when the target type is not `String`
+- binary columns are decoded through `Lynon` when the target type is not `Buffer`
+- `Buffer` targets keep the raw binary payload without Lynon decoding
+- plain text columns are not implicitly treated as JSON
+
 For temporal types, see [time functions](time.md).
 
 ---
@@ -387,6 +416,8 @@ This means:
 
 - do not keep `ResultSet` objects after the transaction block returns
 - materialize rows with `toList()` inside the transaction when they must outlive it
+- the iterable returned by `decodeAs<T>()` is also transaction-scoped
+- decoded objects produced while iterating `decodeAs<T>()` are detached ordinary Lyng values
 
 The same rule applies to generated keys from `ExecutionResult.getGeneratedKeys()`: the `ResultSet` is transaction-scoped, but rows returned by `toList()` are detached.
 

lyngio/src/commonMain/kotlin/net/sergeych/lyng/io/db/SqlRuntimeSupport.kt

@@ -18,21 +18,33 @@
 package net.sergeych.lyng.io.db
 
 import net.sergeych.lyng.Arguments
+import net.sergeych.lyng.DeclAnnotation
 import net.sergeych.lyng.ModuleScope
 import net.sergeych.lyng.Scope
 import net.sergeych.lyng.ScopeFacade
+import net.sergeych.lyng.TypeDecl
 import net.sergeych.lyng.obj.Obj
 import net.sergeych.lyng.obj.ObjBool
+import net.sergeych.lyng.obj.ObjBuffer
+import net.sergeych.lyng.obj.ObjBitBuffer
 import net.sergeych.lyng.obj.ObjClass
 import net.sergeych.lyng.obj.ObjEnumClass
 import net.sergeych.lyng.obj.ObjEnumEntry
 import net.sergeych.lyng.obj.ObjException
 import net.sergeych.lyng.obj.ObjImmutableList
+import net.sergeych.lyng.obj.ObjInstance
 import net.sergeych.lyng.obj.ObjInt
 import net.sergeych.lyng.obj.ObjNull
+import net.sergeych.lyng.obj.ObjRecord
 import net.sergeych.lyng.obj.ObjString
+import net.sergeych.lyng.obj.ObjTypeExpr
+import net.sergeych.lyng.obj.ObjVoid
 import net.sergeych.lyng.obj.thisAs
 import net.sergeych.lyng.requireScope
+import net.sergeych.lyng.serialization.ObjJsonClass
+import net.sergeych.lynon.BitArray
+import net.sergeych.lynon.ObjLynonClass
+import kotlinx.serialization.json.Json
 import kotlin.collections.List
 import kotlin.collections.Map
 import kotlin.collections.MutableList
@@ -43,11 +55,14 @@ import kotlin.collections.forEachIndexed
 import kotlin.collections.getOrNull
 import kotlin.collections.getOrPut
 import kotlin.collections.indices
+import kotlin.collections.LinkedHashMap
 import kotlin.collections.linkedMapOf
 import kotlin.collections.listOf
 import kotlin.collections.map
 import kotlin.collections.mutableListOf
+import kotlin.collections.set
 import kotlin.text.lowercase
+import kotlin.text.substringAfterLast
 
 internal data class SqlColumnMeta(
     val name: String,
@@ -90,6 +105,9 @@ internal class SqlCoreModule private constructor(
     val sqlConstraintException: ObjException.Companion.ExceptionClass,
     val sqlUsageException: ObjException.Companion.ExceptionClass,
     val rollbackException: ObjException.Companion.ExceptionClass,
+    val iterableClass: ObjClass,
+    val iteratorClass: ObjClass,
+    val dbFieldAdapterClass: ObjClass,
     val sqlTypes: SqlTypeEntries,
 ) {
     companion object {
@@ -106,6 +124,11 @@ internal class SqlCoreModule private constructor(
             sqlConstraintException = module.requireClass("SqlConstraintException") as ObjException.Companion.ExceptionClass,
             sqlUsageException = module.requireClass("SqlUsageException") as ObjException.Companion.ExceptionClass,
             rollbackException = module.requireClass("RollbackException") as ObjException.Companion.ExceptionClass,
+            iterableClass = module.importProvider.rootScope.get("Iterable")?.value as? ObjClass
+                ?: error("lyng.stdlib.Iterable declaration is missing"),
+            iteratorClass = module.importProvider.rootScope.get("Iterator")?.value as? ObjClass
+                ?: error("lyng.stdlib.Iterator declaration is missing"),
+            dbFieldAdapterClass = module.requireClass("DbFieldAdapter"),
             sqlTypes = SqlTypeEntries.resolve(module),
         )
     }
@@ -148,6 +171,8 @@ internal class SqlRuntimeTypes private constructor(
     val rowClass: ObjClass,
     val columnClass: ObjClass,
     val executionResultClass: ObjClass,
+    val decodedIterableClass: ObjClass,
+    val decodedIteratorClass: ObjClass,
 ) {
     companion object {
         fun create(prefix: String, core: SqlCoreModule): SqlRuntimeTypes {
@@ -157,6 +182,8 @@ internal class SqlRuntimeTypes private constructor(
             val rowClass = object : ObjClass("${prefix}Row", core.rowClass) {}
             val columnClass = object : ObjClass("${prefix}Column", core.columnClass) {}
             val executionResultClass = object : ObjClass("${prefix}ExecutionResult", core.executionResultClass) {}
+            val decodedIterableClass = object : ObjClass("${prefix}DecodedIterable", core.iterableClass) {}
+            val decodedIteratorClass = object : ObjClass("${prefix}DecodedIterator", core.iteratorClass) {}
             val runtime = SqlRuntimeTypes(
                 core = core,
                 databaseClass = databaseClass,
@@ -165,6 +192,8 @@ internal class SqlRuntimeTypes private constructor(
                 rowClass = rowClass,
                 columnClass = columnClass,
                 executionResultClass = executionResultClass,
+                decodedIterableClass = decodedIterableClass,
+                decodedIteratorClass = decodedIteratorClass,
             )
             runtime.bind()
             return runtime
@@ -251,6 +280,19 @@ internal class SqlRuntimeTypes private constructor(
             self.lifetime.ensureActive(this)
             ObjImmutableList(self.rows)
         }
+        resultSetClass.addFn(
+            "decodeAs",
+            callSignature = core.resultSetClass.getInstanceMemberOrNull("decodeAs")?.callSignature
+        ) {
+            val self = thisAs<SqlResultSetObj>()
+            self.lifetime.ensureActive(this)
+            SqlDecodedIterableObj(
+                self.types,
+                self.lifetime,
+                self.rows.map { it as SqlRowObj },
+                resolveDecodeTargetType(requireScope())
+            )
+        }
 
         rowClass.addProperty("size", getter = {
             val self = thisAs<SqlRowObj>()
@@ -260,6 +302,12 @@ internal class SqlRuntimeTypes private constructor(
             val self = thisAs<SqlRowObj>()
             ObjImmutableList(self.values)
         })
+        rowClass.addFn(
+            "decodeAs",
+            callSignature = core.rowClass.getInstanceMemberOrNull("decodeAs")?.callSignature
+        ) {
+            decodeSqlRow(requireScope(), thisAs(), resolveDecodeTargetType(requireScope()))
+        }
 
         columnClass.addProperty("name", getter = { ObjString(thisAs<SqlColumnObj>().meta.name) })
         columnClass.addProperty("sqlType", getter = { thisAs<SqlColumnObj>().meta.sqlType })
@@ -276,6 +324,27 @@ internal class SqlRuntimeTypes private constructor(
             self.lifetime.ensureActive(this)
             SqlResultSetObj(self.types, self.lifetime, self.result.generatedKeys)
         }
+
+        decodedIterableClass.addFn("iterator") {
+            val self = thisAs<SqlDecodedIterableObj>()
+            self.lifetime.ensureActive(this)
+            SqlDecodedIteratorObj(self.types, self.lifetime, self.rows.iterator(), self.targetType)
+        }
+
+        decodedIteratorClass.addFn("hasNext") {
+            val self = thisAs<SqlDecodedIteratorObj>()
+            self.lifetime.ensureActive(this)
+            ObjBool(self.rows.hasNext())
+        }
+        decodedIteratorClass.addFn("next") {
+            val self = thisAs<SqlDecodedIteratorObj>()
+            self.lifetime.ensureActive(this)
+            decodeSqlRow(requireScope(), self.rows.next(), self.targetType)
+        }
+        decodedIteratorClass.addFn("cancelIteration") {
+            thisAs<SqlDecodedIteratorObj>().lifetime.ensureActive(this)
+            ObjVoid
+        }
     }
 }
 
@@ -319,6 +388,7 @@ internal class SqlResultSetObj(
     val lifetime: SqlTransactionLifetime,
     data: SqlResultSetData,
 ) : Obj() {
+    val columnMeta: List<SqlColumnMeta> = data.columns
     val columns: List<Obj> = data.columns.map { SqlColumnObj(types, it) }
     val rows: List<Obj> = buildRows(types, data)
 
@@ -334,13 +404,14 @@ internal class SqlResultSetObj(
             indexByName.getOrPut(column.name.lowercase()) { mutableListOf() }.add(index)
         }
         return data.rows.map { rowValues ->
-            SqlRowObj(types, rowValues, indexByName)
+            SqlRowObj(types, data.columns, rowValues, indexByName)
         }
     }
 }
 
 internal class SqlRowObj(
     val types: SqlRuntimeTypes,
+    val columns: List<SqlColumnMeta>,
     val values: List<Obj>,
     private val indexByName: Map<String, List<Int>>,
 ) : Obj() {
@@ -381,6 +452,26 @@ internal class SqlRowObj(
     }
 }
 
+internal class SqlDecodedIterableObj(
+    val types: SqlRuntimeTypes,
+    val lifetime: SqlTransactionLifetime,
+    val rows: List<SqlRowObj>,
+    val targetType: TypeDecl,
+) : Obj() {
+    override val objClass: ObjClass
+        get() = types.decodedIterableClass
+}
+
+internal class SqlDecodedIteratorObj(
+    val types: SqlRuntimeTypes,
+    val lifetime: SqlTransactionLifetime,
+    val rows: Iterator<SqlRowObj>,
+    val targetType: TypeDecl,
+) : Obj() {
+    override val objClass: ObjClass
+        get() = types.decodedIteratorClass
+}
+
 internal class SqlColumnObj(
     val types: SqlRuntimeTypes,
     val meta: SqlColumnMeta,
@@ -397,3 +488,339 @@ internal class SqlExecutionResultObj(
     override val objClass: ObjClass
         get() = types.executionResultClass
 }
+
+private fun resolveDecodeTargetType(scope: Scope): TypeDecl {
+    val explicit = scope.args.explicitTypeArgs.singleOrNull()
+    if (explicit != null) return explicit
+    val bound = scope["T"]?.value
+    return when (bound) {
+        is ObjTypeExpr -> bound.typeDecl
+        is ObjClass -> TypeDecl.Simple(bound.className, false)
+        else -> scope.raiseIllegalArgument("decodeAs requires exactly one type argument")
+    }
+}
+
+private suspend fun decodeSqlRow(scope: Scope, row: SqlRowObj, targetType: TypeDecl): Obj {
+    val targetClass = resolveTypeDeclClass(scope, targetType)
+    if (targetClass != null && shouldUseStructuredRowDecoding(row, targetClass)) {
+        return decodeStructuredRow(scope, row, targetType, targetClass)
+    }
+    if (row.values.size == 1) {
+        return decodeSqlValue(scope, row.types, row, row.columns[0], row.values[0], targetType)
+    }
+    scope.raiseError(
+        ObjException(
+            row.types.core.sqlUsageException,
+            scope,
+            ObjString("Can't decode SQL row with ${row.values.size} columns as ${renderTypeName(targetType)}")
+        )
+    )
+}
+
+private fun shouldUseStructuredRowDecoding(row: SqlRowObj, targetClass: ObjClass): Boolean {
+    if (row.values.size > 1) return true
+    val memberNames = linkedMapOf<String, Int>()
+    targetClass.constructorMeta?.params?.forEach { memberNames[it.name.lowercase()] = 1 }
+    row.columns.forEach { column ->
+        if (column.name.lowercase() in memberNames) return true
+    }
+    return false
+}
+
+private suspend fun decodeStructuredRow(
+    scope: Scope,
+    row: SqlRowObj,
+    targetType: TypeDecl,
+    targetClass: ObjClass,
+): Obj {
+    val meta = targetClass.constructorMeta
+        ?: raiseSqlUsage(scope, row.types, "Can't decode SQL row as ${targetClass.className}: target class has no constructor metadata")
+
+    val normalizedColumns = buildColumnLookup(scope, row)
+    val consumed = mutableSetOf<String>()
+    val namedArgs = LinkedHashMap<String, Obj>()
+
+    for (param in meta.params) {
+        if (param.isTransient) continue
+        val lowered = param.name.lowercase()
+        val column = normalizedColumns[lowered]
+        if (column == null) {
+            if (param.defaultValue == null && !param.type.isNullable) {
+                raiseSqlUsage(scope, row.types, "Missing SQL column '${param.name}' for ${targetClass.className}")
+            }
+            continue
+        }
+        namedArgs[param.name] = decodeSqlValue(
+            scope,
+            row.types,
+            row,
+            column.first,
+            row.values[column.second],
+            param.type,
+            param.annotations
+        )
+        consumed += lowered
+    }
+
+    val callScope = scope.createChildScope(args = Arguments(list = emptyList(), named = namedArgs))
+    val instance = targetClass.callOn(callScope)
+    if (instance !is ObjInstance) {
+        return instance
+    }
+    val knownFields = collectSerializableFieldTargets(scope, row, targetClass, instance)
+
+    for ((lowered, target) in knownFields) {
+        if (consumed.contains(lowered)) continue
+        val column = normalizedColumns[lowered] ?: continue
+        val targetTypeDecl = target.record.typeDecl ?: TypeDecl.TypeAny
+        target.record.value = decodeSqlValue(
+            scope,
+            row.types,
+            row,
+            column.first,
+            row.values[column.second],
+            targetTypeDecl,
+            target.annotations
+        )
+        consumed += lowered
+    }
+
+    val allowedNames = meta.params.filter { !it.isTransient }.map { it.name.lowercase() }.toMutableSet()
+    allowedNames += knownFields.keys
+    for (column in row.columns) {
+        val lowered = column.name.lowercase()
+        if (lowered !in allowedNames) {
+            raiseSqlUsage(scope, row.types, "Unknown SQL result column '${column.name}' while decoding ${renderTypeName(targetType)}")
+        }
+    }
+
+    instance.invokeInstanceMethod(scope, "onDeserialized", Arguments.EMPTY) { ObjVoid }
+    return instance
+}
+
+private data class FieldDecodeTarget(
+    val record: ObjRecord,
+    val annotations: List<DeclAnnotation>,
+)
+
+private fun collectSerializableFieldTargets(
+    scope: Scope,
+    row: SqlRowObj,
+    targetClass: ObjClass,
+    instance: ObjInstance,
+): Map<String, FieldDecodeTarget> {
+    val result = linkedMapOf<String, FieldDecodeTarget>()
+    for ((name, record) in instance.serializingVars) {
+        val simpleName = name.substringAfterLast("::")
+        val lowered = simpleName.lowercase()
+        val classAnnotations = targetClass.getInstanceMemberOrNull(simpleName)?.annotations ?: emptyList()
+        val previous = result.put(lowered, FieldDecodeTarget(record, classAnnotations))
+        if (previous != null) {
+            raiseSqlUsage(scope, row.types, "Ambiguous serializable target field '$lowered' in ${targetClass.className}")
+        }
+    }
+    return result
+}
+
+private fun buildColumnLookup(scope: Scope, row: SqlRowObj): Map<String, Pair<SqlColumnMeta, Int>> {
+    val result = linkedMapOf<String, Pair<SqlColumnMeta, Int>>()
+    row.columns.forEachIndexed { index, column ->
+        val lowered = column.name.lowercase()
+        if (result.containsKey(lowered)) {
+            raiseSqlUsage(scope, row.types, "Ambiguous SQL result column: ${column.name}")
+        }
+        result[lowered] = column to index
+    }
+    return result
+}
+
+private suspend fun decodeSqlValue(
+    scope: Scope,
+    types: SqlRuntimeTypes,
+    row: SqlRowObj,
+    column: SqlColumnMeta,
+    value: Obj,
+    targetType: TypeDecl,
+    annotations: List<DeclAnnotation> = emptyList(),
+): Obj {
+    val adapterAnnotation = findDbDecodeWithAnnotation(scope, types, annotations)
+    if (adapterAnnotation != null) {
+        val adapted = applyDbFieldAdapter(scope, types, row, column, value, targetType, adapterAnnotation)
+        if (adapted === ObjNull) {
+            if (targetType.isNullable || targetType == TypeDecl.TypeNullableAny) return ObjNull
+            raiseSqlUsage(scope, types, "SQL column '${column.name}' is null but target type ${renderTypeName(targetType)} is non-null")
+        }
+        if (!matchesTypeDeclCompat(scope, adapted, targetType)) {
+            raiseSqlUsage(
+                scope,
+                types,
+                "DB adapter result for column '${column.name}' does not match target type ${renderTypeName(targetType)}"
+            )
+        }
+        return adapted
+    }
+    if (value === ObjNull) {
+        if (targetType.isNullable || targetType == TypeDecl.TypeNullableAny) return ObjNull
+        raiseSqlUsage(scope, types, "SQL column '${column.name}' is null but target type ${renderTypeName(targetType)} is non-null")
+    }
+    if (matchesTypeDeclCompat(scope, value, targetType)) {
+        return value
+    }
+    if (value is ObjBuffer) {
+        return try {
+            val decoded = ObjLynonClass.decodeAny(scope, ObjBitBuffer(BitArray(value.byteArray, 8)))
+            if (!matchesTypeDeclCompat(scope, decoded, targetType)) {
+                raiseSqlUsage(
+                    scope,
+                    types,
+                    "Lynon-decoded SQL column '${column.name}' does not match target type ${renderTypeName(targetType)}"
+                )
+            }
+            decoded
+        } catch (e: Throwable) {
+            raiseSqlUsage(
+                scope,
+                types,
+                "Failed to decode Lynon column '${column.name}' as ${renderTypeName(targetType)}: ${e.message ?: e::class.simpleName}"
+            )
+        }
+    }
+    if (isJsonLikeNativeType(column.nativeType) && value is ObjString) {
+        return try {
+            ObjJsonClass.decodeFromJsonElement(scope, Json.parseToJsonElement(value.value), targetType)
+        } catch (e: Throwable) {
+            raiseSqlUsage(
+                scope,
+                types,
+                "Failed to decode JSON column '${column.name}' as ${renderTypeName(targetType)}: ${e.message ?: e::class.simpleName}"
+            )
+        }
+    }
+    raiseSqlUsage(
+        scope,
+        types,
+        "SQL column '${column.name}' of native type ${column.nativeType} can't be decoded as ${renderTypeName(targetType)}"
+    )
+}
+
+private fun findDbDecodeWithAnnotation(
+    scope: Scope,
+    types: SqlRuntimeTypes,
+    annotations: List<DeclAnnotation>,
+): DeclAnnotation? {
+    val matches = annotations.filter { it.name == "DbDecodeWith" }
+    if (matches.size > 1) {
+        raiseSqlUsage(scope, types, "Only one @DbDecodeWith(...) annotation is allowed per declaration")
+    }
+    return matches.singleOrNull()
+}
+
+private suspend fun applyDbFieldAdapter(
+    scope: Scope,
+    types: SqlRuntimeTypes,
+    row: SqlRowObj,
+    column: SqlColumnMeta,
+    value: Obj,
+    targetType: TypeDecl,
+    annotation: DeclAnnotation,
+): Obj {
+    if (annotation.named.isNotEmpty() || annotation.positional.size != 1) {
+        raiseSqlUsage(scope, types, "@DbDecodeWith(...) expects exactly one adapter instance argument")
+    }
+    val adapter = annotation.positional.first()
+    if (!adapter.isInstanceOf(types.core.dbFieldAdapterClass)) {
+        raiseSqlUsage(scope, types, "@DbDecodeWith(...) argument must implement DbFieldAdapter")
+    }
+    return try {
+        adapter.invokeInstanceMethod(
+            scope,
+            "decode",
+            Arguments(
+                value,
+                SqlColumnObj(types, column),
+                row,
+                runtimeTargetTypeObject(scope, targetType)
+            )
+        )
+    } catch (e: Throwable) {
+        raiseSqlUsage(
+            scope,
+            types,
+            "Failed to decode SQL column '${column.name}' with @DbDecodeWith(...): ${e.message ?: e::class.simpleName}"
+        )
+    }
+}
+
+private fun runtimeTargetTypeObject(scope: Scope, targetType: TypeDecl): Obj {
+    return resolveTypeDeclClass(scope, targetType) ?: ObjTypeExpr(targetType)
+}
+
+private fun isJsonLikeNativeType(nativeType: String): Boolean {
+    val normalized = nativeType.trim().substringBefore('(').lowercase()
+    return normalized == "json" || normalized == "jsonb"
+}
+
+private fun resolveTypeDeclClass(scope: Scope, type: TypeDecl): ObjClass? = when (type) {
+    is TypeDecl.Simple -> {
+        val direct = scope[type.name]?.value as? ObjClass
+        direct ?: scope[type.name.substringAfterLast('.')]?.value as? ObjClass
+    }
+    is TypeDecl.Generic -> {
+        val direct = scope[type.name]?.value as? ObjClass
+        direct ?: scope[type.name.substringAfterLast('.')]?.value as? ObjClass
+    }
+    is TypeDecl.Ellipsis -> resolveTypeDeclClass(scope, type.elementType)
+    is TypeDecl.TypeVar -> when (val bound = scope[type.name]?.value) {
+        is ObjClass -> bound
+        is ObjTypeExpr -> resolveTypeDeclClass(scope, bound.typeDecl)
+        else -> null
+    }
+    else -> null
+}
+
+private fun matchesTypeDeclCompat(scope: Scope, value: Obj, typeDecl: TypeDecl): Boolean {
+    if (value === ObjNull) return typeDecl.isNullable || typeDecl == TypeDecl.TypeNullableAny
+    fun resolve(typeName: String): ObjClass? {
+        val direct = scope[typeName]?.value as? ObjClass
+        return direct ?: scope[typeName.substringAfterLast('.')]?.value as? ObjClass
+    }
+    return when (typeDecl) {
+        TypeDecl.TypeAny, TypeDecl.TypeNullableAny -> true
+        is TypeDecl.TypeVar -> {
+            val cls = resolve(typeDecl.name)
+            if (cls != null) value.isInstanceOf(cls) else value.isInstanceOf(typeDecl.name)
+        }
+        is TypeDecl.Simple -> {
+            val cls = resolve(typeDecl.name)
+            if (cls != null) value.isInstanceOf(cls) else value.isInstanceOf(typeDecl.name.substringAfterLast('.'))
+        }
+        is TypeDecl.Generic -> {
+            val cls = resolve(typeDecl.name)
+            if (cls != null) value.isInstanceOf(cls) else value.isInstanceOf(typeDecl.name.substringAfterLast('.'))
+        }
+        is TypeDecl.Function -> value.isInstanceOf("Callable")
+        is TypeDecl.Ellipsis -> matchesTypeDeclCompat(scope, value, typeDecl.elementType)
+        is TypeDecl.Union -> typeDecl.options.any { matchesTypeDeclCompat(scope, value, it) }
+        is TypeDecl.Intersection -> typeDecl.options.all { matchesTypeDeclCompat(scope, value, it) }
+    }
+}
+
+private fun renderTypeName(type: TypeDecl): String = when (type) {
+    TypeDecl.TypeAny -> "Object"
+    TypeDecl.TypeNullableAny -> "Object?"
+    is TypeDecl.Simple -> type.name + if (type.isNullable) "?" else ""
+    is TypeDecl.Generic -> type.name + "<" + type.args.joinToString(",") { renderTypeName(it) } + ">" + if (type.isNullable) "?" else ""
+    is TypeDecl.Function -> "Callable"
+    is TypeDecl.Ellipsis -> renderTypeName(type.elementType) + "..."
+    is TypeDecl.TypeVar -> type.name + if (type.isNullable) "?" else ""
+    is TypeDecl.Union -> type.options.joinToString(" | ") { renderTypeName(it) } + if (type.isNullable) "?" else ""
+    is TypeDecl.Intersection -> type.options.joinToString(" & ") { renderTypeName(it) } + if (type.isNullable) "?" else ""
+}
+
+private fun raiseSqlUsage(scope: Scope, types: SqlRuntimeTypes?, message: String): Nothing {
+    val exClass = types?.core?.sqlUsageException
+    if (exClass != null) {
+        scope.raiseError(ObjException(exClass, scope, ObjString(message)))
+    }
+    scope.raiseIllegalArgument(message)
+}

lyngio/src/jvmTest/kotlin/net/sergeych/lyng/io/db/sqlite/LyngSqliteModuleTest.kt

@@ -137,6 +137,230 @@ class LyngSqliteModuleTest {
         assertEquals(2L, result.value)
     }
 
+    @Test
+    fun testDecodeAsProjectsJsonColumnIntoObjectField() = runTest {
+        val scope = Script.newScope()
+        createSqliteModule(scope.importManager)
+
+        val code = """
+            import lyng.io.db.sqlite
+
+            class Point(x: Int, y: Int)
+            class Row(id: Int, payload: Point)
+
+            val db = openSqlite(":memory:")
+            db.transaction { tx ->
+                tx.execute("create table data(id integer not null, payload json not null)")
+                tx.execute("insert into data(id, payload) values(?, ?)", 7, "{\"x\":4,\"y\":5}")
+                val row = tx.select("select id, payload from data").decodeAs<Row>().first
+                assertEquals(7, row.id)
+                assertEquals(4, row.payload.x)
+                assertEquals(5, row.payload.y)
+                row.payload.y
+            }
+        """.trimIndent()
+
+        val result = Compiler.compile(Source("<sqlite-decode-json-field>", code), scope.importManager).execute(scope) as ObjInt
+        assertEquals(5L, result.value)
+    }
+
+    @Test
+    fun testDecodeAsSupportsSingleJsonColumnProjection() = runTest {
+        val scope = Script.newScope()
+        createSqliteModule(scope.importManager)
+
+        val code = """
+            import lyng.io.db.sqlite
+
+            class Point(x: Int, y: Int)
+
+            val db = openSqlite(":memory:")
+            db.transaction { tx ->
+                tx.execute("create table data(payload json not null)")
+                tx.execute("insert into data(payload) values(?)", "{\"x\":9,\"y\":11}")
+                val point = tx.select("select payload from data").decodeAs<Point>().first
+                assertEquals(9, point.x)
+                assertEquals(11, point.y)
+                point.x + point.y
+            }
+        """.trimIndent()
+
+        val result = Compiler.compile(Source("<sqlite-decode-json-single>", code), scope.importManager).execute(scope) as ObjInt
+        assertEquals(20L, result.value)
+    }
+
+    @Test
+    fun testDecodeAsDoesNotAutoDecodePlainTextAsJson() = runTest {
+        val scope = Script.newScope()
+        createSqliteModule(scope.importManager)
+
+        val code = """
+            import lyng.io.db.sqlite
+
+            class Point(x: Int, y: Int)
+
+            val db = openSqlite(":memory:")
+            db.transaction { tx ->
+                tx.execute("create table data(payload text not null)")
+                tx.execute("insert into data(payload) values(?)", "{\"x\":1,\"y\":2}")
+                tx.select("select payload from data").decodeAs<Point>().first
+            }
+        """.trimIndent()
+
+        val error = assertFailsWith<ExecutionError> {
+            Compiler.compile(Source("<sqlite-decode-json-text-guard>", code), scope.importManager).execute(scope)
+        }
+        assertEquals("SqlUsageException", error.errorObject.objClass.className)
+    }
+
+    @Test
+    fun testDecodeAsSupportsSingleLynonBinaryProjection() = runTest {
+        val scope = Script.newScope()
+        createSqliteModule(scope.importManager)
+
+        val code = """
+            import lyng.io.db.sqlite
+            import lyng.serialization
+
+            class Point(x: Int, y: Int)
+
+            val db = openSqlite(":memory:")
+            db.transaction { tx ->
+                tx.execute("create table data(payload blob not null)")
+                tx.execute("insert into data(payload) values(?)", Lynon.encode(Point(6, 8)).toBuffer())
+                val point = tx.select("select payload from data").decodeAs<Point>().first
+                assertEquals(6, point.x)
+                assertEquals(8, point.y)
+                point.x + point.y
+            }
+        """.trimIndent()
+
+        val result = Compiler.compile(Source("<sqlite-decode-lynon-single>", code), scope.importManager).execute(scope) as ObjInt
+        assertEquals(14L, result.value)
+    }
+
+    @Test
+    fun testDecodeAsSupportsDbDecodeWithOnConstructorParamsAndFields() = runTest {
+        val scope = Script.newScope()
+        createSqliteModule(scope.importManager)
+
+        val code = """
+            import lyng.io.db
+            import lyng.io.db.sqlite
+
+            object TrimmedStringAdapter: DbFieldAdapter {
+                override fun decode(rawValue, column, row, targetType) =
+                    when(rawValue) {
+                        null -> null
+                        else -> rawValue.toString().trim()
+                    }
+            }
+
+            class User(
+                id: Int,
+                @DbDecodeWith(TrimmedStringAdapter) name: String
+            ) {
+                @DbDecodeWith(TrimmedStringAdapter)
+                var note: String = ""
+            }
+
+            val db = openSqlite(":memory:")
+            db.transaction { tx ->
+                tx.execute("create table data(id integer not null, name text not null, note text not null)")
+                tx.execute("insert into data(id, name, note) values(?, ?, ?)", 10, "  Alice  ", "  hello  ")
+                val user = tx.select("select id, name, note from data").decodeAs<User>().first
+                assertEquals(10, user.id)
+                assertEquals("Alice", user.name)
+                assertEquals("hello", user.note)
+                user.note.size
+            }
+        """.trimIndent()
+
+        val result = Compiler.compile(Source("<sqlite-decode-dbdecodewith>", code), scope.importManager).execute(scope) as ObjInt
+        assertEquals(5L, result.value)
+    }
+
+    @Test
+    fun testDecodeAsFailsWhenDbDecodeWithReturnsWrongType() = runTest {
+        val scope = Script.newScope()
+        createSqliteModule(scope.importManager)
+
+        val code = """
+            import lyng.io.db
+            import lyng.io.db.sqlite
+
+            object BadAdapter: DbFieldAdapter {
+                override fun decode(rawValue, column, row, targetType) = 42
+            }
+
+            class User(@DbDecodeWith(BadAdapter) name: String)
+
+            val db = openSqlite(":memory:")
+            db.transaction { tx ->
+                tx.execute("create table data(name text not null)")
+                tx.execute("insert into data(name) values(?)", "Alice")
+                tx.select("select name from data").decodeAs<User>().first
+            }
+        """.trimIndent()
+
+        val error = assertFailsWith<ExecutionError> {
+            Compiler.compile(Source("<sqlite-decode-dbdecodewith-bad-type>", code), scope.importManager).execute(scope)
+        }
+        assertEquals("SqlUsageException", error.errorObject.objClass.className)
+    }
+
+    @Test
+    fun testDecodeAsKeepsRawBufferForBufferTarget() = runTest {
+        val scope = Script.newScope()
+        createSqliteModule(scope.importManager)
+
+        val code = """
+            import lyng.io.db.sqlite
+            import lyng.buffer
+            import lyng.serialization
+
+            class Point(x: Int, y: Int)
+
+            val db = openSqlite(":memory:")
+            db.transaction { tx ->
+                tx.execute("create table data(payload blob not null)")
+                val encoded = Lynon.encode(Point(1, 2)).toBuffer()
+                tx.execute("insert into data(payload) values(?)", encoded)
+                val payload = tx.select("select payload from data").decodeAs<Buffer>().first
+                assertEquals(encoded.size, payload.size)
+                payload.size
+            }
+        """.trimIndent()
+
+        val result = Compiler.compile(Source("<sqlite-decode-buffer-raw>", code), scope.importManager).execute(scope) as ObjInt
+        assertTrue(result.value > 0)
+    }
+
+    @Test
+    fun testDecodeAsFailsForNonLynonBinaryTypedProjection() = runTest {
+        val scope = Script.newScope()
+        createSqliteModule(scope.importManager)
+
+        val code = """
+            import lyng.io.db.sqlite
+            import lyng.buffer
+
+            class Point(x: Int, y: Int)
+
+            val db = openSqlite(":memory:")
+            db.transaction { tx ->
+                tx.execute("create table data(payload blob not null)")
+                tx.execute("insert into data(payload) values(?)", "hello".encodeUtf8())
+                tx.select("select payload from data").decodeAs<Point>().first
+            }
+        """.trimIndent()
+
+        val error = assertFailsWith<ExecutionError> {
+            Compiler.compile(Source("<sqlite-decode-lynon-binary-guard>", code), scope.importManager).execute(scope)
+        }
+        assertEquals("SqlUsageException", error.errorObject.objClass.className)
+    }
+
     @Test
     fun testNestedTransactionRollbackUsesSavepoint() = runTest {
         val scope = Script.newScope()

lyngio/src/linuxTest/kotlin/net/sergeych/lyng/io/db/sqlite/LyngSqliteModuleNativeTest.kt

@@ -19,11 +19,13 @@ package net.sergeych.lyng.io.db.sqlite
 
 import kotlinx.coroutines.test.runTest
 import kotlinx.datetime.TimeZone
+import net.sergeych.lyng.Compiler
 import net.sergeych.lyng.ExecutionError
 import net.sergeych.lyng.ModuleScope
 import net.sergeych.lyng.Pos
 import net.sergeych.lyng.Scope
 import net.sergeych.lyng.Script
+import net.sergeych.lyng.Source
 import net.sergeych.lyng.obj.Obj
 import net.sergeych.lyng.obj.ObjBool
 import net.sergeych.lyng.obj.ObjBuffer
@@ -231,6 +233,230 @@ class LyngSqliteModuleNativeTest {
         assertEquals("beta", stringValue(scope, rows.getAt(scope, ObjInt.of(1)).getAt(scope, ObjString("name"))))
     }
 
+    @Test
+    fun testDecodeAsProjectsJsonColumnIntoObjectField() = runTest {
+        val scope = Script.newScope()
+        createSqliteModule(scope.importManager)
+
+        val code = """
+            import lyng.io.db.sqlite
+
+            class Point(x: Int, y: Int)
+            class Row(id: Int, payload: Point)
+
+            val db = openSqlite(":memory:")
+            db.transaction { tx ->
+                tx.execute("create table data(id integer not null, payload json not null)")
+                tx.execute("insert into data(id, payload) values(?, ?)", 7, "{\"x\":4,\"y\":5}")
+                val row = tx.select("select id, payload from data").decodeAs<Row>().first
+                assertEquals(7, row.id)
+                assertEquals(4, row.payload.x)
+                assertEquals(5, row.payload.y)
+                row.payload.y
+            }
+        """.trimIndent()
+
+        val result = Compiler.compile(Source("<sqlite-native-decode-json-field>", code), scope.importManager).execute(scope) as ObjInt
+        assertEquals(5L, result.value)
+    }
+
+    @Test
+    fun testDecodeAsSupportsSingleJsonColumnProjection() = runTest {
+        val scope = Script.newScope()
+        createSqliteModule(scope.importManager)
+
+        val code = """
+            import lyng.io.db.sqlite
+
+            class Point(x: Int, y: Int)
+
+            val db = openSqlite(":memory:")
+            db.transaction { tx ->
+                tx.execute("create table data(payload json not null)")
+                tx.execute("insert into data(payload) values(?)", "{\"x\":9,\"y\":11}")
+                val point = tx.select("select payload from data").decodeAs<Point>().first
+                assertEquals(9, point.x)
+                assertEquals(11, point.y)
+                point.x + point.y
+            }
+        """.trimIndent()
+
+        val result = Compiler.compile(Source("<sqlite-native-decode-json-single>", code), scope.importManager).execute(scope) as ObjInt
+        assertEquals(20L, result.value)
+    }
+
+    @Test
+    fun testDecodeAsDoesNotAutoDecodePlainTextAsJson() = runTest {
+        val scope = Script.newScope()
+        createSqliteModule(scope.importManager)
+
+        val code = """
+            import lyng.io.db.sqlite
+
+            class Point(x: Int, y: Int)
+
+            val db = openSqlite(":memory:")
+            db.transaction { tx ->
+                tx.execute("create table data(payload text not null)")
+                tx.execute("insert into data(payload) values(?)", "{\"x\":1,\"y\":2}")
+                tx.select("select payload from data").decodeAs<Point>().first
+            }
+        """.trimIndent()
+
+        val error = assertFailsWith<ExecutionError> {
+            Compiler.compile(Source("<sqlite-native-decode-json-text-guard>", code), scope.importManager).execute(scope)
+        }
+        assertEquals("SqlUsageException", error.errorObject.objClass.className)
+    }
+
+    @Test
+    fun testDecodeAsSupportsSingleLynonBinaryProjection() = runTest {
+        val scope = Script.newScope()
+        createSqliteModule(scope.importManager)
+
+        val code = """
+            import lyng.io.db.sqlite
+            import lyng.serialization
+
+            class Point(x: Int, y: Int)
+
+            val db = openSqlite(":memory:")
+            db.transaction { tx ->
+                tx.execute("create table data(payload blob not null)")
+                tx.execute("insert into data(payload) values(?)", Lynon.encode(Point(6, 8)).toBuffer())
+                val point = tx.select("select payload from data").decodeAs<Point>().first
+                assertEquals(6, point.x)
+                assertEquals(8, point.y)
+                point.x + point.y
+            }
+        """.trimIndent()
+
+        val result = Compiler.compile(Source("<sqlite-native-decode-lynon-single>", code), scope.importManager).execute(scope) as ObjInt
+        assertEquals(14L, result.value)
+    }
+
+    @Test
+    fun testDecodeAsSupportsDbDecodeWithOnConstructorParamsAndFields() = runTest {
+        val scope = Script.newScope()
+        createSqliteModule(scope.importManager)
+
+        val code = """
+            import lyng.io.db
+            import lyng.io.db.sqlite
+
+            object TrimmedStringAdapter: DbFieldAdapter {
+                override fun decode(rawValue, column, row, targetType) =
+                    when(rawValue) {
+                        null -> null
+                        else -> rawValue.toString().trim()
+                    }
+            }
+
+            class User(
+                id: Int,
+                @DbDecodeWith(TrimmedStringAdapter) name: String
+            ) {
+                @DbDecodeWith(TrimmedStringAdapter)
+                var note: String = ""
+            }
+
+            val db = openSqlite(":memory:")
+            db.transaction { tx ->
+                tx.execute("create table data(id integer not null, name text not null, note text not null)")
+                tx.execute("insert into data(id, name, note) values(?, ?, ?)", 10, "  Alice  ", "  hello  ")
+                val user = tx.select("select id, name, note from data").decodeAs<User>().first
+                assertEquals(10, user.id)
+                assertEquals("Alice", user.name)
+                assertEquals("hello", user.note)
+                user.note.size
+            }
+        """.trimIndent()
+
+        val result = Compiler.compile(Source("<sqlite-native-decode-dbdecodewith>", code), scope.importManager).execute(scope) as ObjInt
+        assertEquals(5L, result.value)
+    }
+
+    @Test
+    fun testDecodeAsFailsWhenDbDecodeWithReturnsWrongType() = runTest {
+        val scope = Script.newScope()
+        createSqliteModule(scope.importManager)
+
+        val code = """
+            import lyng.io.db
+            import lyng.io.db.sqlite
+
+            object BadAdapter: DbFieldAdapter {
+                override fun decode(rawValue, column, row, targetType) = 42
+            }
+
+            class User(@DbDecodeWith(BadAdapter) name: String)
+
+            val db = openSqlite(":memory:")
+            db.transaction { tx ->
+                tx.execute("create table data(name text not null)")
+                tx.execute("insert into data(name) values(?)", "Alice")
+                tx.select("select name from data").decodeAs<User>().first
+            }
+        """.trimIndent()
+
+        val error = assertFailsWith<ExecutionError> {
+            Compiler.compile(Source("<sqlite-native-decode-dbdecodewith-bad-type>", code), scope.importManager).execute(scope)
+        }
+        assertEquals("SqlUsageException", error.errorObject.objClass.className)
+    }
+
+    @Test
+    fun testDecodeAsKeepsRawBufferForBufferTarget() = runTest {
+        val scope = Script.newScope()
+        createSqliteModule(scope.importManager)
+
+        val code = """
+            import lyng.io.db.sqlite
+            import lyng.buffer
+            import lyng.serialization
+
+            class Point(x: Int, y: Int)
+
+            val db = openSqlite(":memory:")
+            db.transaction { tx ->
+                tx.execute("create table data(payload blob not null)")
+                val encoded = Lynon.encode(Point(1, 2)).toBuffer()
+                tx.execute("insert into data(payload) values(?)", encoded)
+                val payload = tx.select("select payload from data").decodeAs<Buffer>().first
+                assertEquals(encoded.size, payload.size)
+                payload.size
+            }
+        """.trimIndent()
+
+        val result = Compiler.compile(Source("<sqlite-native-decode-buffer-raw>", code), scope.importManager).execute(scope) as ObjInt
+        assertTrue(result.value > 0)
+    }
+
+    @Test
+    fun testDecodeAsFailsForNonLynonBinaryTypedProjection() = runTest {
+        val scope = Script.newScope()
+        createSqliteModule(scope.importManager)
+
+        val code = """
+            import lyng.io.db.sqlite
+            import lyng.buffer
+
+            class Point(x: Int, y: Int)
+
+            val db = openSqlite(":memory:")
+            db.transaction { tx ->
+                tx.execute("create table data(payload blob not null)")
+                tx.execute("insert into data(payload) values(?)", "hello".encodeUtf8())
+                tx.select("select payload from data").decodeAs<Point>().first
+            }
+        """.trimIndent()
+
+        val error = assertFailsWith<ExecutionError> {
+            Compiler.compile(Source("<sqlite-native-decode-lynon-binary-guard>", code), scope.importManager).execute(scope)
+        }
+        assertEquals("SqlUsageException", error.errorObject.objClass.className)
+    }
+
     @Test
     fun testExecuteRejectsReturningButSelectSupportsIt() = runTest {
         val scope = Script.newScope()

lyngio/stdlib/lyng/io/db.lyng

@@ -20,6 +20,32 @@ extern class SqlColumn {
     val nativeType: String
 }
 
+/*
+    Adapter interface for custom DB field projection.
+
+    Use it with `@DbDecodeWith(adapter)` on class constructor parameters or
+    class-body fields/properties participating in `decodeAs<T>()` projection.
+
+    `targetType` is the requested Lyng target type represented as a runtime
+    type object, such as a class or a type expression.
+
+    Default methods throw `NotImplementedException`.
+*/
+interface DbFieldAdapter {
+    /*
+        Decode one raw database field value into a Lyng value suitable for the
+        requested target type.
+    */
+    fun decode(rawValue: Object?, column: SqlColumn, row: SqlRow, targetType: Object): Object? =
+        throw NotImplementedException("DB field adapter decode is not implemented")
+
+    /*
+        Encode one Lyng value into a database field representation.
+    */
+    fun encode(value: Object?, targetType: Object): Object? =
+        throw NotImplementedException("DB field adapter encode is not implemented")
+}
+
 extern class SqlRow {
     /* Number of columns in the row */
     val size: Int
@@ -34,6 +60,22 @@ extern class SqlRow {
         names and invalid indexes should also fail.
     */
     override fun getAt(indexOrName: String | Int): Object?
+
+    /*
+        Decode this row into a typed Lyng value.
+
+        For object/class targets, constructor parameters are matched by column
+        label first and then remaining matching serializable mutable fields are
+        assigned.
+
+        If a constructor parameter or class-body field/property has
+        `@DbDecodeWith(adapter)`, the adapter is applied first and its result
+        must match the target member type.
+
+        For single-column rows, the column value may also be decoded directly to
+        the requested target type.
+    */
+    fun decodeAs<T>(): T
 }
 
 /*
@@ -69,6 +111,16 @@ extern class ResultSet : Iterable<SqlRow> {
         internally, but this must not change visible later iteration behavior.
     */
     override fun isEmpty(): Bool
+
+    /*
+        Return a transaction-scoped iterable view that decodes each row with
+        `SqlRow.decodeAs<T>()`.
+
+        The returned iterable itself must not be used after the owning
+        transaction ends. Materialized decoded objects may outlive the
+        transaction.
+    */
+    fun decodeAs<T>(): Iterable<T>
 }
 
 extern class ExecutionResult {

lynglib/src/commonMain/kotlin/net/sergeych/lyng/ArgsDeclaration.kt

@@ -88,7 +88,8 @@ data class ArgsDeclaration(val params: List<Item>, val endTokenType: Token.Type)
                         a.visibility ?: defaultVisibility,
                         recordType = recordType,
                         declaringClass = declaringClass,
-                        isTransient = a.isTransient
+                        isTransient = a.isTransient,
+                        annotations = a.annotations
                     )
                 }
                 return
@@ -108,7 +109,8 @@ data class ArgsDeclaration(val params: List<Item>, val endTokenType: Token.Type)
                 a.visibility ?: defaultVisibility,
                 recordType = recordType,
                 declaringClass = declaringClass,
-                isTransient = a.isTransient
+                isTransient = a.isTransient,
+                annotations = a.annotations
             )
         }
 
@@ -505,5 +507,7 @@ data class ArgsDeclaration(val params: List<Item>, val endTokenType: Token.Type)
         val accessType: AccessType? = null,
         val visibility: Visibility? = null,
         val isTransient: Boolean = false,
+        val annotationSpecs: List<ParsedDeclAnnotation> = emptyList(),
+        val annotations: List<DeclAnnotation> = emptyList(),
     )
 }

lynglib/src/commonMain/kotlin/net/sergeych/lyng/ClassDeclStatement.kt

@@ -41,6 +41,17 @@ data class ClassDeclSpec(
     val initScope: List<Statement>,
 )
 
+private suspend fun evaluateConstructorAnnotations(scope: Scope, args: ArgsDeclaration?): ArgsDeclaration? {
+    if (args == null) return null
+    if (args.params.none { it.annotationSpecs.isNotEmpty() }) return args
+    return args.copy(
+        params = args.params.map { item ->
+            if (item.annotationSpecs.isEmpty()) item
+            else item.copy(annotations = item.annotationSpecs.evaluateDeclAnnotations(scope))
+        }
+    )
+}
+
 internal suspend fun executeClassDecl(
     scope: Scope,
     spec: ClassDeclSpec,
@@ -61,7 +72,7 @@ internal suspend fun executeClassDecl(
         val newClass = ObjInstanceClass(spec.className, *parentClasses.toTypedArray())
         newClass.isAnonymous = spec.isAnonymous
         newClass.isSingletonObject = true
-        newClass.constructorMeta = ArgsDeclaration(emptyList(), Token.Type.RPAREN)
+        newClass.constructorMeta = evaluateConstructorAnnotations(scope, ArgsDeclaration(emptyList(), Token.Type.RPAREN))
         for (i in parentClasses.indices) {
             val argsList = spec.baseSpecs[i].args
             if (argsList != null) newClass.directParentArgs[parentClasses[i]] = argsList
@@ -86,6 +97,7 @@ internal suspend fun executeClassDecl(
     }
 
     if (spec.isExtern) {
+        val evaluatedConstructorArgs = evaluateConstructorAnnotations(scope, spec.constructorArgs)
         val parentClasses = spec.baseSpecs.mapNotNull { baseSpec ->
             val rec = scope[baseSpec.name]
             val cls = rec?.value as? ObjClass
@@ -106,8 +118,8 @@ internal suspend fun executeClassDecl(
         }
         val stub = resolved ?: ObjInstanceClass(spec.className, *parentClasses.toTypedArray()).apply {
             this.isAbstract = true
-            constructorMeta = spec.constructorArgs
-            spec.constructorArgs?.params?.forEach { p ->
+            constructorMeta = evaluatedConstructorArgs
+            evaluatedConstructorArgs?.params?.forEach { p ->
                 if (p.accessType != null) {
                     createField(
                         p.name,
@@ -118,6 +130,7 @@ internal suspend fun executeClassDecl(
                         pos = Pos.builtIn,
                         isTransient = p.isTransient,
                         type = ObjRecord.Type.ConstructorField,
+                        annotations = p.annotations,
                         fieldId = spec.constructorFieldIds?.get(p.name)
                     )
                 }
@@ -161,16 +174,17 @@ internal suspend fun executeClassDecl(
         }
     }
 
+    val evaluatedConstructorArgs = evaluateConstructorAnnotations(scope, spec.constructorArgs)
     val newClass = ObjInstanceClass(spec.className, *parentClasses.toTypedArray()).also {
         it.isAbstract = spec.isAbstract
         it.isClosed = spec.isClosed
         it.instanceConstructor = constructorCode
-        it.constructorMeta = spec.constructorArgs
+        it.constructorMeta = evaluatedConstructorArgs
         for (i in parentClasses.indices) {
             val argsList = spec.baseSpecs[i].args
             if (argsList != null) it.directParentArgs[parentClasses[i]] = argsList
         }
-        spec.constructorArgs?.params?.forEach { p ->
+        evaluatedConstructorArgs?.params?.forEach { p ->
             if (p.accessType != null) {
                 it.createField(
                     p.name,
@@ -181,6 +195,7 @@ internal suspend fun executeClassDecl(
                     pos = Pos.builtIn,
                     isTransient = p.isTransient,
                     type = ObjRecord.Type.ConstructorField,
+                    annotations = p.annotations,
                     fieldId = spec.constructorFieldIds?.get(p.name)
                 )
             }

lynglib/src/commonMain/kotlin/net/sergeych/lyng/ClassInstanceDeclStatements.kt

@@ -38,6 +38,7 @@ class ClassInstanceFieldDeclStatement(
     val isClosed: Boolean,
     val isOverride: Boolean,
     val isTransient: Boolean,
+    val annotationSpecs: List<ParsedDeclAnnotation> = emptyList(),
     val fieldId: Int?,
     val initStatement: Statement?,
     override val pos: Pos,
@@ -56,6 +57,7 @@ class ClassInstancePropertyDeclStatement(
     val isClosed: Boolean,
     val isOverride: Boolean,
     val isTransient: Boolean,
+    val annotationSpecs: List<ParsedDeclAnnotation> = emptyList(),
     val prop: ObjProperty,
     val methodId: Int?,
     val initStatement: Statement?,
@@ -75,6 +77,7 @@ class ClassInstanceDelegatedDeclStatement(
     val isClosed: Boolean,
     val isOverride: Boolean,
     val isTransient: Boolean,
+    val annotationSpecs: List<ParsedDeclAnnotation> = emptyList(),
     val methodId: Int?,
     val initStatement: Statement?,
     override val pos: Pos,

lynglib/src/commonMain/kotlin/net/sergeych/lyng/ClassStaticFieldInitStatement.kt

@@ -32,6 +32,7 @@ class ClassStaticFieldInitStatement(
     val initializer: Statement?,
     val isDelegated: Boolean,
     val isTransient: Boolean,
+    val annotationSpecs: List<ParsedDeclAnnotation> = emptyList(),
     private val startPos: Pos,
 ) : Statement() {
     override val pos: Pos = startPos
@@ -39,6 +40,7 @@ class ClassStaticFieldInitStatement(
     override suspend fun execute(scope: Scope): Obj {
         val initValue = initializer?.let { execBytecodeOnly(scope, it, "class static field init") }?.byValueCopy()
             ?: ObjNull
+        val annotations = annotationSpecs.evaluateDeclAnnotations(scope)
         val cls = scope.thisObj as? ObjClass
             ?: scope.raiseIllegalState("static field init requires class scope")
         return if (isDelegated) {
@@ -61,7 +63,8 @@ class ClassStaticFieldInitStatement(
                 writeVisibility,
                 startPos,
                 isTransient = isTransient,
-                type = ObjRecord.Type.Delegated
+                type = ObjRecord.Type.Delegated,
+                annotations = annotations
             ).apply {
                 delegate = finalDelegate
             }
@@ -72,7 +75,8 @@ class ClassStaticFieldInitStatement(
                 visibility,
                 writeVisibility,
                 recordType = ObjRecord.Type.Delegated,
-                isTransient = isTransient
+                isTransient = isTransient,
+                annotations = annotations
             ).apply {
                 delegate = finalDelegate
             }
@@ -85,7 +89,8 @@ class ClassStaticFieldInitStatement(
                 visibility,
                 writeVisibility,
                 startPos,
-                isTransient = isTransient
+                isTransient = isTransient,
+                annotations = annotations
             )
             scope.addItem(
                 name,
@@ -94,7 +99,8 @@ class ClassStaticFieldInitStatement(
                 visibility,
                 writeVisibility,
                 recordType = ObjRecord.Type.Field,
-                isTransient = isTransient
+                isTransient = isTransient,
+                annotations = annotations
             )
             initValue
         }

lynglib/src/commonMain/kotlin/net/sergeych/lyng/Compiler.kt

@@ -2014,6 +2014,7 @@ class Compiler(
 
     private var lastAnnotation: (suspend (Scope, ObjString, Statement) -> Statement)? = null
     private var isTransientFlag: Boolean = false
+    private val pendingDeclAnnotations: MutableList<ParsedDeclAnnotation> = mutableListOf()
     private var lastLabel: String? = null
     private val strictSlotRefs: Boolean = settings.strictSlotRefs
     private val allowUnresolvedRefs: Boolean = settings.allowUnresolvedRefs
@@ -2689,6 +2690,7 @@ class Compiler(
         lastAnnotation = null
         lastLabel = null
         isTransientFlag = false
+        pendingDeclAnnotations.clear()
         while (true) {
             val t = cc.next()
             return when (t.type) {
@@ -2706,15 +2708,17 @@ class Compiler(
                 }
 
                 Token.Type.ATLABEL -> {
-                    val label = t.value
-                    if (label == "Transient") {
+                    val parsedAnnotation = parseDeclAnnotation(t)
+                    if (parsedAnnotation.name == "Transient") {
                         isTransientFlag = true
-                        continue
                     }
                     if (cc.peekNextNonWhitespace().type == Token.Type.LBRACE) {
-                        lastLabel = label
+                        lastLabel = parsedAnnotation.name
+                    }
+                    pendingDeclAnnotations += parsedAnnotation
+                    if (parsedAnnotation.name != "Transient") {
+                        lastAnnotation = parsedAnnotation.toStatementAnnotation()
                     }
-                    lastAnnotation = parseAnnotation(t)
                     continue
                 }
 
@@ -4033,11 +4037,17 @@ class Compiler(
 
                 Token.Type.ID, Token.Type.ATLABEL -> {
                     var isTransient = false
-                    if (t.type == Token.Type.ATLABEL) {
-                        if (t.value == "Transient") {
+                    val annotationSpecs = mutableListOf<ParsedDeclAnnotation>()
+                    while (t.type == Token.Type.ATLABEL) {
+                        val spec = parseDeclAnnotation(t)
+                        annotationSpecs += spec
+                        if (spec.name == "Transient") {
                             isTransient = true
-                            t = cc.next()
-                        } else throw ScriptError(t.pos, "Unexpected label in argument list")
+                        }
+                        t = cc.next()
+                    }
+                    if (annotationSpecs.isNotEmpty() && !isClassDeclaration) {
+                        throw ScriptError(t.pos, "parameter annotations are currently supported only on class constructor parameters")
                     }
 
                     // visibility
@@ -4114,7 +4124,8 @@ class Compiler(
                         defaultValue,
                         effectiveAccess,
                         visibility,
-                        isTransient
+                        isTransient,
+                        annotationSpecs = annotationSpecs
                     )
 
                     // important: valid argument list continues with ',' and ends with '->' or ')'
@@ -7120,19 +7131,25 @@ class Compiler(
         return parseNumberOrNull(isPlus) ?: throw ScriptError(cc.currentPos(), "Expecting number")
     }
 
-    suspend fun parseAnnotation(t: Token): (suspend (Scope, ObjString, Statement) -> Statement) {
+    private suspend fun parseDeclAnnotation(t: Token): ParsedDeclAnnotation {
         val extraArgs = parseArgsOrNull()
         resolutionSink?.reference(t.value, t.pos)
-//        println("annotation ${t.value}: args: $extraArgs")
-        return { scope, name, body ->
-            val extras = extraArgs?.first?.toArguments(scope, extraArgs.second)?.list
-            val required = listOf(name, body)
-            val args = extras?.let { required + it } ?: required
-            val fn = scope.get(t.value)?.value ?: scope.raiseSymbolNotFound("annotation not found: ${t.value}")
-            if (fn !is Statement) scope.raiseIllegalArgument("annotation must be callable, got ${fn.objClass}")
-            (fn.execute(scope.createChildScope(Arguments(args))) as? Statement)
-                ?: scope.raiseClassCastError("function annotation must return callable")
-        }
+        val compiledArgs = extraArgs?.first?.map { arg ->
+            val value = arg.value
+            arg.copy(
+                value = if (value is Statement) wrapBytecode(value) else value
+            )
+        } ?: emptyList()
+        return ParsedDeclAnnotation(
+            name = t.value,
+            args = compiledArgs,
+            tailBlockMode = extraArgs?.second ?: false,
+            pos = t.pos
+        )
+    }
+
+    suspend fun parseAnnotation(t: Token): (suspend (Scope, ObjString, Statement) -> Statement) {
+        return parseDeclAnnotation(t).toStatementAnnotation()
     }
 
     suspend fun parseArgsOrNull(): Pair<List<ParsedArgument>, Boolean>? =
@@ -9232,6 +9249,8 @@ class Compiler(
         isTransient: Boolean = isTransientFlag
     ): Statement {
         isTransientFlag = false
+        val declarationAnnotationSpecs = pendingDeclAnnotations.toList()
+        pendingDeclAnnotations.clear()
         val actualExtern = isExtern || (codeContexts.lastOrNull() as? CodeContext.ClassBody)?.isExtern == true
         var start = cc.currentPos()
         var extTypeName: String? = null
@@ -9700,6 +9719,7 @@ class Compiler(
                     isClosed = isClosed,
                     isOverride = isOverride,
                     isTransient = isTransient,
+                    annotations = emptyList(),
                     accessTypeLabel = "Callable",
                     initializer = initExpr,
                     pos = start
@@ -10251,6 +10271,8 @@ class Compiler(
         isTransient: Boolean = isTransientFlag
     ): Statement {
         isTransientFlag = false
+        val declarationAnnotationSpecs = pendingDeclAnnotations.toList()
+        pendingDeclAnnotations.clear()
         val actualExtern = isExtern || (codeContexts.lastOrNull() as? CodeContext.ClassBody)?.isExtern == true
         val markStart = cc.savePos()
         val nextToken = cc.next()
@@ -10643,6 +10665,9 @@ class Compiler(
             !isStatic &&
             !isProperty
         ) {
+            if (declarationAnnotationSpecs.isNotEmpty()) {
+                throw ScriptError(start, "declaration annotations are currently supported only on class members")
+            }
             if (isDelegate) {
                 val initExpr = initialExpression ?: throw ScriptError(start, "Delegate must be initialized")
                 val slotPlan = slotPlanStack.lastOrNull()
@@ -10663,6 +10688,9 @@ class Compiler(
         }
 
         if (isStatic) {
+            if (extTypeName != null && declarationAnnotationSpecs.isNotEmpty()) {
+                throw ScriptError(start, "declaration annotations are not supported on extension properties")
+            }
             if (declaringClassNameCaptured != null) {
                 val directRef = unwrapDirectRef(initialExpression)
                 val declClass = resolveTypeDeclObjClass(varTypeDecl)
@@ -10685,6 +10713,7 @@ class Compiler(
                 initializer = initialExpression,
                 isDelegated = isDelegate,
                 isTransient = isTransient,
+                annotationSpecs = declarationAnnotationSpecs,
                 startPos = start
             )
             return NopStatement
@@ -10847,6 +10876,9 @@ class Compiler(
         }
 
         if (extTypeName != null) {
+            if (declarationAnnotationSpecs.isNotEmpty()) {
+                throw ScriptError(start, "declaration annotations are not supported on extension properties")
+            }
             declareLocalName(extensionPropertyGetterName(extTypeName, name), isMutable = false)
             if (setter != null) {
                 declareLocalName(extensionPropertySetterName(extTypeName, name), isMutable = false)
@@ -10883,6 +10915,7 @@ class Compiler(
                         isClosed = isClosed,
                         isOverride = isOverride,
                         isTransient = isTransient,
+                        annotations = emptyList(),
                         accessTypeLabel = accessType,
                         initializer = initExpr,
                         pos = start
@@ -10898,6 +10931,7 @@ class Compiler(
                     isClosed = isClosed,
                     isOverride = isOverride,
                     isTransient = isTransient,
+                    annotationSpecs = declarationAnnotationSpecs,
                     methodId = memberMethodId,
                     initStatement = initStmt,
                     pos = start
@@ -10919,6 +10953,7 @@ class Compiler(
                         isClosed = isClosed,
                         isOverride = isOverride,
                         isTransient = isTransient,
+                        annotations = emptyList(),
                         prop = prop,
                         pos = start
                     )
@@ -10933,6 +10968,7 @@ class Compiler(
                     isClosed = isClosed,
                     isOverride = isOverride,
                     isTransient = isTransient,
+                    annotationSpecs = declarationAnnotationSpecs,
                     prop = prop,
                     methodId = memberMethodId,
                     initStatement = initStmt,
@@ -10950,6 +10986,7 @@ class Compiler(
                     isClosed = isClosed,
                     isOverride = isOverride,
                     isTransient = isTransient,
+                    annotations = emptyList(),
                     isLateInitVal = isLateInitVal,
                     initializer = initialExpression,
                     pos = start
@@ -10966,6 +11003,7 @@ class Compiler(
                 isClosed = isClosed,
                 isOverride = isOverride,
                 isTransient = isTransient,
+                annotationSpecs = declarationAnnotationSpecs,
                 fieldId = memberFieldId,
                 initStatement = initStmt,
                 pos = start

lynglib/src/commonMain/kotlin/net/sergeych/lyng/DeclAnnotation.kt

@@ -0,0 +1,129 @@
+/*
+ * Copyright 2026 Sergey S. Chernov real.sergeych@gmail.com
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package net.sergeych.lyng
+
+import net.sergeych.lyng.bytecode.BytecodeStatement
+import net.sergeych.lyng.obj.Obj
+import net.sergeych.lyng.obj.ObjIterable
+import net.sergeych.lyng.obj.ObjList
+import net.sergeych.lyng.obj.ObjMap
+import net.sergeych.lyng.obj.ObjString
+
+/**
+ * Preserved declaration annotation evaluated at declaration-creation time.
+ */
+data class DeclAnnotation(
+    val name: String,
+    val positional: List<Obj> = emptyList(),
+    val named: Map<String, Obj> = emptyMap(),
+)
+
+/**
+ * Parsed declaration annotation awaiting declaration-time evaluation.
+ */
+data class ParsedDeclAnnotation(
+    val name: String,
+    val args: List<ParsedArgument> = emptyList(),
+    val tailBlockMode: Boolean = false,
+    val pos: Pos = Pos.builtIn,
+) {
+    suspend fun evaluate(scope: Scope): DeclAnnotation {
+        val resolved = evaluateDeclAnnotationArguments(scope, args, tailBlockMode)
+        return DeclAnnotation(name, resolved.list, resolved.named)
+    }
+
+    fun toStatementAnnotation(): suspend (Scope, ObjString, Statement) -> Statement = { scope, declName, body ->
+        val extras = args.toArguments(scope, tailBlockMode).list
+        val required = listOf(declName, body)
+        val callArgs = if (extras.isEmpty()) required else required + extras
+        val fn = scope.get(name)?.value ?: scope.raiseSymbolNotFound("annotation not found: $name")
+        if (fn !is Statement) scope.raiseIllegalArgument("annotation must be callable, got ${fn.objClass}")
+        (fn.execute(scope.createChildScope(Arguments(callArgs))) as? Statement)
+            ?: scope.raiseClassCastError("function annotation must return callable")
+    }
+}
+
+suspend fun Iterable<ParsedDeclAnnotation>.evaluateDeclAnnotations(scope: Scope): List<DeclAnnotation> {
+    val result = mutableListOf<DeclAnnotation>()
+    for (spec in this) {
+        result += spec.evaluate(scope)
+    }
+    return result
+}
+
+private suspend fun evaluateDeclAnnotationArguments(
+    scope: Scope,
+    args: List<ParsedArgument>,
+    tailBlockMode: Boolean,
+): Arguments {
+    suspend fun eval(value: Obj): Obj = when (value) {
+        is BytecodeBodyProvider -> (value.bytecodeBody() ?: scope.raiseIllegalState("annotation argument requires bytecode body")).execute(scope)
+        is Statement -> BytecodeStatement.wrap(value, "@annotation", allowLocalSlots = true).execute(scope)
+        else -> value.callOn(scope)
+    }
+
+    val resolved = ArrayList<ParsedArgument>(args.size)
+    for (arg in args) {
+        resolved += arg.copy(value = eval(arg.value))
+    }
+
+    val positional: MutableList<Obj> = mutableListOf()
+    var named: MutableMap<String, Obj>? = null
+    var namedSeen = false
+    for ((idx, x) in resolved.withIndex()) {
+        if (x.name != null) {
+            if (named == null) named = linkedMapOf()
+            if (named.containsKey(x.name)) scope.raiseIllegalArgument("argument '${x.name}' is already set")
+            named[x.name] = x.value
+            namedSeen = true
+            continue
+        }
+        val value = x.value
+        if (x.isSplat) {
+            when {
+                value is ObjMap -> {
+                    if (named == null) named = linkedMapOf()
+                    for ((k, v) in value.map) {
+                        if (k !is ObjString) scope.raiseIllegalArgument("named splat expects a Map with string keys")
+                        val key = k.value
+                        if (named.containsKey(key)) scope.raiseIllegalArgument("argument '$key' is already set")
+                        named[key] = v
+                    }
+                    namedSeen = true
+                }
+                value is ObjList -> {
+                    if (namedSeen) scope.raiseIllegalArgument("positional splat cannot follow named arguments")
+                    positional.addAll(value.list)
+                }
+                value.isInstanceOf(ObjIterable) -> {
+                    if (namedSeen) scope.raiseIllegalArgument("positional splat cannot follow named arguments")
+                    val iterable = value.invokeInstanceMethod(scope, "toList") as ObjList
+                    positional.addAll(iterable.list)
+                }
+                else -> scope.raiseClassCastError("expected list of objects for splat argument")
+            }
+        } else {
+            val isLast = idx == resolved.size - 1
+            if (namedSeen && !(isLast && tailBlockMode)) {
+                scope.raiseIllegalArgument("positional argument cannot follow named arguments")
+            }
+            positional.add(value)
+        }
+    }
+    return Arguments(positional, tailBlockMode, named ?: emptyMap())
+}

lynglib/src/commonMain/kotlin/net/sergeych/lyng/InstanceInitStatements.kt

@@ -33,6 +33,7 @@ class InstanceFieldInitStatement(
     val isClosed: Boolean,
     val isOverride: Boolean,
     val isTransient: Boolean,
+    val annotations: List<DeclAnnotation> = emptyList(),
     val isLateInitVal: Boolean,
     val initializer: Statement?,
     override val pos: Pos,
@@ -50,7 +51,8 @@ class InstanceFieldInitStatement(
             isAbstract = isAbstract,
             isClosed = isClosed,
             isOverride = isOverride,
-            isTransient = isTransient
+            isTransient = isTransient,
+            annotations = annotations
         )
         return ObjVoid
     }
@@ -74,6 +76,7 @@ class InstancePropertyInitStatement(
     val isClosed: Boolean,
     val isOverride: Boolean,
     val isTransient: Boolean,
+    val annotations: List<DeclAnnotation> = emptyList(),
     val prop: ObjProperty,
     override val pos: Pos,
 ) : Statement() {
@@ -88,7 +91,8 @@ class InstancePropertyInitStatement(
             isAbstract = isAbstract,
             isClosed = isClosed,
             isOverride = isOverride,
-            isTransient = isTransient
+            isTransient = isTransient,
+            annotations = annotations
         )
         return ObjVoid
     }
@@ -104,6 +108,7 @@ class InstanceDelegatedInitStatement(
     val isClosed: Boolean,
     val isOverride: Boolean,
     val isTransient: Boolean,
+    val annotations: List<DeclAnnotation> = emptyList(),
     val accessTypeLabel: String,
     val initializer: Statement,
     override val pos: Pos,
@@ -130,7 +135,8 @@ class InstanceDelegatedInitStatement(
             isAbstract = isAbstract,
             isClosed = isClosed,
             isOverride = isOverride,
-            isTransient = isTransient
+            isTransient = isTransient,
+            annotations = annotations
         ).apply {
             delegate = finalDelegate
         }

lynglib/src/commonMain/kotlin/net/sergeych/lyng/Scope.kt

@@ -718,6 +718,7 @@ open class Scope(
         isTransient: Boolean = false,
         callSignature: CallSignature? = null,
         typeDecl: TypeDecl? = null,
+        annotations: List<DeclAnnotation> = emptyList(),
         fieldId: Int? = null,
         methodId: Int? = null
     ): ObjRecord {
@@ -731,6 +732,7 @@ open class Scope(
             isTransient = isTransient,
             callSignature = callSignature,
             typeDecl = typeDecl,
+            annotations = annotations,
             memberName = name,
             fieldId = fieldId,
             methodId = methodId

lynglib/src/commonMain/kotlin/net/sergeych/lyng/bytecode/BytecodeCompiler.kt

@@ -6360,7 +6360,8 @@ class BytecodeCompiler(
                     isMutable = stmt.isMutable,
                     visibility = stmt.visibility,
                     writeVisibility = stmt.writeVisibility,
-                    isTransient = stmt.isTransient
+                    isTransient = stmt.isTransient,
+                    annotationSpecs = stmt.annotationSpecs
                 )
             )
         } else {
@@ -6370,7 +6371,8 @@ class BytecodeCompiler(
                     isMutable = stmt.isMutable,
                     visibility = stmt.visibility,
                     writeVisibility = stmt.writeVisibility,
-                    isTransient = stmt.isTransient
+                    isTransient = stmt.isTransient,
+                    annotationSpecs = stmt.annotationSpecs
                 )
             )
         }
@@ -6397,6 +6399,7 @@ class BytecodeCompiler(
                 writeVisibility = stmt.writeVisibility,
                 typeDecl = stmt.typeDecl,
                 isTransient = stmt.isTransient,
+                annotationSpecs = stmt.annotationSpecs,
                 isAbstract = stmt.isAbstract,
                 isClosed = stmt.isClosed,
                 isOverride = stmt.isOverride,
@@ -6419,6 +6422,7 @@ class BytecodeCompiler(
                 visibility = stmt.visibility,
                 writeVisibility = stmt.writeVisibility,
                 isTransient = stmt.isTransient,
+                annotationSpecs = stmt.annotationSpecs,
                 isAbstract = stmt.isAbstract,
                 isClosed = stmt.isClosed,
                 isOverride = stmt.isOverride,
@@ -6442,6 +6446,7 @@ class BytecodeCompiler(
                 visibility = stmt.visibility,
                 writeVisibility = stmt.writeVisibility,
                 isTransient = stmt.isTransient,
+                annotationSpecs = stmt.annotationSpecs,
                 isAbstract = stmt.isAbstract,
                 isClosed = stmt.isClosed,
                 isOverride = stmt.isOverride,
@@ -6475,6 +6480,7 @@ class BytecodeCompiler(
                 visibility = stmt.visibility,
                 writeVisibility = stmt.writeVisibility,
                 isTransient = stmt.isTransient,
+                annotations = stmt.annotations,
                 isAbstract = stmt.isAbstract,
                 isClosed = stmt.isClosed,
                 isOverride = stmt.isOverride
@@ -6497,6 +6503,7 @@ class BytecodeCompiler(
                 visibility = stmt.visibility,
                 writeVisibility = stmt.writeVisibility,
                 isTransient = stmt.isTransient,
+                annotations = stmt.annotations,
                 isAbstract = stmt.isAbstract,
                 isClosed = stmt.isClosed,
                 isOverride = stmt.isOverride
@@ -6517,6 +6524,7 @@ class BytecodeCompiler(
                 visibility = stmt.visibility,
                 writeVisibility = stmt.writeVisibility,
                 isTransient = stmt.isTransient,
+                annotations = stmt.annotations,
                 isAbstract = stmt.isAbstract,
                 isClosed = stmt.isClosed,
                 isOverride = stmt.isOverride,

lynglib/src/commonMain/kotlin/net/sergeych/lyng/bytecode/BytecodeConst.kt

@@ -18,6 +18,7 @@
 package net.sergeych.lyng.bytecode
 
 import net.sergeych.lyng.ArgsDeclaration
+import net.sergeych.lyng.ParsedDeclAnnotation
 import net.sergeych.lyng.Pos
 import net.sergeych.lyng.TypeDecl
 import net.sergeych.lyng.Visibility
@@ -85,6 +86,7 @@ sealed class BytecodeConst {
         val visibility: Visibility,
         val writeVisibility: Visibility?,
         val isTransient: Boolean,
+        val annotationSpecs: List<ParsedDeclAnnotation>,
     ) : BytecodeConst()
     data class ClassDelegatedDecl(
         val name: String,
@@ -92,6 +94,7 @@ sealed class BytecodeConst {
         val visibility: Visibility,
         val writeVisibility: Visibility?,
         val isTransient: Boolean,
+        val annotationSpecs: List<ParsedDeclAnnotation>,
     ) : BytecodeConst()
     data class ClassInstanceInitDecl(
         val initStatement: Obj,
@@ -103,6 +106,7 @@ sealed class BytecodeConst {
         val writeVisibility: Visibility?,
         val typeDecl: TypeDecl?,
         val isTransient: Boolean,
+        val annotationSpecs: List<ParsedDeclAnnotation>,
         val isAbstract: Boolean,
         val isClosed: Boolean,
         val isOverride: Boolean,
@@ -116,6 +120,7 @@ sealed class BytecodeConst {
         val visibility: Visibility,
         val writeVisibility: Visibility?,
         val isTransient: Boolean,
+        val annotationSpecs: List<ParsedDeclAnnotation>,
         val isAbstract: Boolean,
         val isClosed: Boolean,
         val isOverride: Boolean,
@@ -130,6 +135,7 @@ sealed class BytecodeConst {
         val visibility: Visibility,
         val writeVisibility: Visibility?,
         val isTransient: Boolean,
+        val annotationSpecs: List<ParsedDeclAnnotation>,
         val isAbstract: Boolean,
         val isClosed: Boolean,
         val isOverride: Boolean,
@@ -143,6 +149,7 @@ sealed class BytecodeConst {
         val visibility: Visibility,
         val writeVisibility: Visibility?,
         val isTransient: Boolean,
+        val annotations: List<net.sergeych.lyng.DeclAnnotation>,
         val isAbstract: Boolean,
         val isClosed: Boolean,
         val isOverride: Boolean,
@@ -153,6 +160,7 @@ sealed class BytecodeConst {
         val visibility: Visibility,
         val writeVisibility: Visibility?,
         val isTransient: Boolean,
+        val annotations: List<net.sergeych.lyng.DeclAnnotation>,
         val isAbstract: Boolean,
         val isClosed: Boolean,
         val isOverride: Boolean,
@@ -164,6 +172,7 @@ sealed class BytecodeConst {
         val visibility: Visibility,
         val writeVisibility: Visibility?,
         val isTransient: Boolean,
+        val annotations: List<net.sergeych.lyng.DeclAnnotation>,
         val isAbstract: Boolean,
         val isClosed: Boolean,
         val isOverride: Boolean,

lynglib/src/commonMain/kotlin/net/sergeych/lyng/bytecode/BytecodeStatement.kt

@@ -365,6 +365,7 @@ class BytecodeStatement private constructor(
                         stmt.initializer?.let { unwrapDeep(it) },
                         stmt.isDelegated,
                         stmt.isTransient,
+                        stmt.annotationSpecs,
                         stmt.pos
                     )
                 }
@@ -385,6 +386,7 @@ class BytecodeStatement private constructor(
                         stmt.isClosed,
                         stmt.isOverride,
                         stmt.isTransient,
+                        stmt.annotationSpecs,
                         stmt.fieldId,
                         stmt.initStatement?.let { unwrapDeep(it) },
                         stmt.pos
@@ -400,6 +402,7 @@ class BytecodeStatement private constructor(
                         stmt.isClosed,
                         stmt.isOverride,
                         stmt.isTransient,
+                        stmt.annotationSpecs,
                         stmt.prop,
                         stmt.methodId,
                         stmt.initStatement?.let { unwrapDeep(it) },
@@ -416,6 +419,7 @@ class BytecodeStatement private constructor(
                         stmt.isClosed,
                         stmt.isOverride,
                         stmt.isTransient,
+                        stmt.annotationSpecs,
                         stmt.methodId,
                         stmt.initStatement?.let { unwrapDeep(it) },
                         stmt.pos
@@ -431,6 +435,7 @@ class BytecodeStatement private constructor(
                         stmt.isClosed,
                         stmt.isOverride,
                         stmt.isTransient,
+                        stmt.annotations,
                         stmt.isLateInitVal,
                         stmt.initializer?.let { unwrapDeep(it) },
                         stmt.pos
@@ -446,6 +451,7 @@ class BytecodeStatement private constructor(
                         stmt.isClosed,
                         stmt.isOverride,
                         stmt.isTransient,
+                        stmt.annotations,
                         stmt.prop,
                         stmt.pos
                     )
@@ -461,6 +467,7 @@ class BytecodeStatement private constructor(
                         stmt.isClosed,
                         stmt.isOverride,
                         stmt.isTransient,
+                        stmt.annotations,
                         stmt.accessTypeLabel,
                         unwrapDeep(stmt.initializer),
                         stmt.pos

lynglib/src/commonMain/kotlin/net/sergeych/lyng/bytecode/CmdRuntime.kt

@@ -2805,6 +2805,7 @@ class CmdDeclClassField(internal val constId: Int, internal val slot: Int) : Cmd
         val decl = frame.fn.constants[constId] as? BytecodeConst.ClassFieldDecl
             ?: error("DECL_CLASS_FIELD expects ClassFieldDecl at $constId")
         val scope = frame.ensureScope()
+        val annotations = decl.annotationSpecs.evaluateDeclAnnotations(scope)
         val cls = scope.thisObj as? ObjClass
             ?: scope.raiseIllegalState("class field init requires class scope")
         val value = frame.slotToObj(slot).byValueCopy()
@@ -2815,7 +2816,8 @@ class CmdDeclClassField(internal val constId: Int, internal val slot: Int) : Cmd
             decl.visibility,
             decl.writeVisibility,
             Pos.builtIn,
-            isTransient = decl.isTransient
+            isTransient = decl.isTransient,
+            annotations = annotations
         )
         scope.addItem(
             decl.name,
@@ -2824,7 +2826,8 @@ class CmdDeclClassField(internal val constId: Int, internal val slot: Int) : Cmd
             decl.visibility,
             decl.writeVisibility,
             recordType = ObjRecord.Type.Field,
-            isTransient = decl.isTransient
+            isTransient = decl.isTransient,
+            annotations = annotations
         )
         return
     }
@@ -2835,6 +2838,7 @@ class CmdDeclClassDelegated(internal val constId: Int, internal val slot: Int) :
         val decl = frame.fn.constants[constId] as? BytecodeConst.ClassDelegatedDecl
             ?: error("DECL_CLASS_DELEGATED expects ClassDelegatedDecl at $constId")
         val scope = frame.ensureScope()
+        val annotations = decl.annotationSpecs.evaluateDeclAnnotations(scope)
         val cls = scope.thisObj as? ObjClass
             ?: scope.raiseIllegalState("class delegated init requires class scope")
         val initValue = frame.slotToObj(slot)
@@ -2857,7 +2861,8 @@ class CmdDeclClassDelegated(internal val constId: Int, internal val slot: Int) :
             decl.writeVisibility,
             Pos.builtIn,
             isTransient = decl.isTransient,
-            type = ObjRecord.Type.Delegated
+            type = ObjRecord.Type.Delegated,
+            annotations = annotations
         ).apply {
             delegate = finalDelegate
         }
@@ -2868,7 +2873,8 @@ class CmdDeclClassDelegated(internal val constId: Int, internal val slot: Int) :
             decl.visibility,
             decl.writeVisibility,
             recordType = ObjRecord.Type.Delegated,
-            isTransient = decl.isTransient
+            isTransient = decl.isTransient,
+            annotations = annotations
         ).apply {
             delegate = finalDelegate
         }
@@ -2895,6 +2901,7 @@ class CmdDeclClassInstanceField(internal val constId: Int, internal val slot: In
         val decl = frame.fn.constants[constId] as? BytecodeConst.ClassInstanceFieldDecl
             ?: error("DECL_CLASS_INSTANCE_FIELD expects ClassInstanceFieldDecl at $constId")
         val scope = frame.ensureScope()
+        val annotations = decl.annotationSpecs.evaluateDeclAnnotations(scope)
         val cls = scope.thisObj as? ObjClass
             ?: scope.raiseIllegalState("class instance field requires class scope")
         cls.createField(
@@ -2911,7 +2918,8 @@ class CmdDeclClassInstanceField(internal val constId: Int, internal val slot: In
             isTransient = decl.isTransient,
             typeDecl = decl.typeDecl,
             type = ObjRecord.Type.Field,
-            fieldId = decl.fieldId
+            fieldId = decl.fieldId,
+            annotations = annotations
         )
         if (!decl.isAbstract) {
             decl.initStatement?.let { cls.instanceInitializers += it }
@@ -2926,6 +2934,7 @@ class CmdDeclClassInstanceProperty(internal val constId: Int, internal val slot:
         val decl = frame.fn.constants[constId] as? BytecodeConst.ClassInstancePropertyDecl
             ?: error("DECL_CLASS_INSTANCE_PROPERTY expects ClassInstancePropertyDecl at $constId")
         val scope = frame.ensureScope()
+        val annotations = decl.annotationSpecs.evaluateDeclAnnotations(scope)
         val cls = scope.thisObj as? ObjClass
             ?: scope.raiseIllegalState("class instance property requires class scope")
         cls.addProperty(
@@ -2938,7 +2947,8 @@ class CmdDeclClassInstanceProperty(internal val constId: Int, internal val slot:
             isOverride = decl.isOverride,
             pos = decl.pos,
             prop = decl.prop,
-            methodId = decl.methodId
+            methodId = decl.methodId,
+            annotations = annotations
         )
         if (!decl.isAbstract) {
             decl.initStatement?.let { cls.instanceInitializers += it }
@@ -2953,6 +2963,7 @@ class CmdDeclClassInstanceDelegated(internal val constId: Int, internal val slot
         val decl = frame.fn.constants[constId] as? BytecodeConst.ClassInstanceDelegatedDecl
             ?: error("DECL_CLASS_INSTANCE_DELEGATED expects ClassInstanceDelegatedDecl at $constId")
         val scope = frame.ensureScope()
+        val annotations = decl.annotationSpecs.evaluateDeclAnnotations(scope)
         val cls = scope.thisObj as? ObjClass
             ?: scope.raiseIllegalState("class instance delegated requires class scope")
         cls.createField(
@@ -2968,7 +2979,8 @@ class CmdDeclClassInstanceDelegated(internal val constId: Int, internal val slot
             isOverride = decl.isOverride,
             isTransient = decl.isTransient,
             type = ObjRecord.Type.Delegated,
-            methodId = decl.methodId
+            methodId = decl.methodId,
+            annotations = annotations
         )
         if (!decl.isAbstract) {
             decl.initStatement?.let { cls.instanceInitializers += it }
@@ -2994,7 +3006,8 @@ class CmdDeclInstanceField(internal val constId: Int, internal val slot: Int) :
             isAbstract = decl.isAbstract,
             isClosed = decl.isClosed,
             isOverride = decl.isOverride,
-            isTransient = decl.isTransient
+            isTransient = decl.isTransient,
+            annotations = decl.annotations
         )
         if (slot >= frame.fn.scopeSlotCount) {
             val localIndex = slot - frame.fn.scopeSlotCount
@@ -3023,7 +3036,8 @@ class CmdDeclInstanceProperty(internal val constId: Int, internal val slot: Int)
             isAbstract = decl.isAbstract,
             isClosed = decl.isClosed,
             isOverride = decl.isOverride,
-            isTransient = decl.isTransient
+            isTransient = decl.isTransient,
+            annotations = decl.annotations
         )
         if (slot >= frame.fn.scopeSlotCount) {
             val localIndex = slot - frame.fn.scopeSlotCount
@@ -3076,7 +3090,8 @@ class CmdDeclInstanceDelegated(internal val constId: Int, internal val slot: Int
             isAbstract = decl.isAbstract,
             isClosed = decl.isClosed,
             isOverride = decl.isOverride,
-            isTransient = decl.isTransient
+            isTransient = decl.isTransient,
+            annotations = decl.annotations
         ).apply {
             delegate = finalDelegate
         }
@@ -3705,9 +3720,26 @@ class CmdGetClassScope(
             decl = declared
             break
         }
-        val resolved = rec ?: scope.raiseSymbolNotFound(name)
-        val declClass = decl ?: cls
-        val resolvedRec = cls.resolveRecord(scope, resolved, name, declClass)
+        val resolvedRec = if (rec != null) {
+            val declClass = decl ?: cls
+            cls.resolveRecord(scope, rec, name, declClass)
+        } else {
+            val metaRec = cls.objClass.getInstanceMemberOrNull(name)
+            if (metaRec == null || metaRec.isAbstract) {
+                scope.raiseSymbolNotFound(name)
+            }
+            val declClass = metaRec.declaringClass ?: cls.objClass
+            val resolved = cls.resolveRecord(scope, metaRec, name, declClass)
+            if (resolved.type == ObjRecord.Type.Fun) {
+                resolved.copy(
+                    value = ObjExternCallable.fromBridge {
+                        resolved.value.invoke(scope, cls, args, declClass)
+                    }
+                )
+            } else {
+                resolved
+            }
+        }
         val value = resolvedRec.value
         frame.storeObjResult(dst, value)
         return

lynglib/src/commonMain/kotlin/net/sergeych/lyng/obj/ObjClass.kt

@@ -28,6 +28,23 @@ import net.sergeych.lynon.LynonType
 // Simple id generator for class identities (not thread-safe; fine for scripts)
 private object ClassIdGen { var c: Long = 1L; fun nextId(): Long = c++ }
 
+private fun DeclAnnotation.toObj(): Obj {
+    val namedArgs = linkedMapOf<Obj, Obj>()
+    for ((k, v) in named) {
+        namedArgs[ObjString(k)] = v
+    }
+    return ObjMap(
+        linkedMapOf(
+            ObjString("name") to ObjString(name),
+            ObjString("positional") to ObjImmutableList(positional),
+            ObjString("named") to ObjMap(namedArgs)
+        )
+    )
+}
+
+private fun annotationListObj(annotations: List<DeclAnnotation>): Obj =
+    ObjImmutableList(annotations.map { it.toObj() })
+
 val ObjClassType by lazy {
     object : ObjClass("Class") {
         override suspend fun deserialize(scope: Scope, decoder: LynonDecoder, lynonType: LynonType?): Obj {
@@ -98,6 +115,30 @@ val ObjClassType by lazy {
             val rec = cls.getInstanceMemberOrNull(name)
             rec?.value ?: ObjNull
         }
+        addFnDoc(
+            name = "getConstructorAnnotations",
+            doc = "Return preserved annotations for a constructor parameter by name as descriptor maps with fields `name`, `positional`, and `named`.",
+            params = listOf(ParamDoc("name", type("lyng.String"))),
+            returns = TypeGenericDoc(type("lyng.List"), listOf(type("lyng.Map"))),
+            moduleName = "lyng.stdlib"
+        ) {
+            val cls = thisAs<ObjClass>()
+            val name = requiredArg<ObjString>(0).value
+            val param = cls.constructorMeta?.params?.firstOrNull { it.name == name }
+            annotationListObj(param?.annotations ?: emptyList())
+        }
+        addFnDoc(
+            name = "getMemberAnnotations",
+            doc = "Return preserved annotations for a member by name as descriptor maps with fields `name`, `positional`, and `named`.",
+            params = listOf(ParamDoc("name", type("lyng.String"))),
+            returns = TypeGenericDoc(type("lyng.List"), listOf(type("lyng.Map"))),
+            moduleName = "lyng.stdlib"
+        ) {
+            val cls = thisAs<ObjClass>()
+            val name = requiredArg<ObjString>(0).value
+            val rec = cls.getInstanceMemberOrNull(name) ?: cls.classScope?.objects?.get(name)
+            annotationListObj(rec?.annotations ?: emptyList())
+        }
     }
 }
 
@@ -851,6 +892,7 @@ open class ObjClass(
         methodId: Int? = null,
         typeDecl: net.sergeych.lyng.TypeDecl? = null,
         callSignature: net.sergeych.lyng.CallSignature? = null,
+        annotations: List<DeclAnnotation> = emptyList(),
     ): ObjRecord {
         // Validation of override rules: only for non-system declarations
         var existing: ObjRecord? = null
@@ -953,6 +995,7 @@ open class ObjClass(
             type = type,
             callSignature = callSignature,
             typeDecl = typeDecl,
+            annotations = annotations,
             memberName = name,
             fieldId = effectiveFieldId,
             methodId = effectiveMethodId
@@ -979,7 +1022,8 @@ open class ObjClass(
         type: ObjRecord.Type = ObjRecord.Type.Field,
         fieldId: Int? = null,
         methodId: Int? = null,
-        callSignature: net.sergeych.lyng.CallSignature? = null
+        callSignature: net.sergeych.lyng.CallSignature? = null,
+        annotations: List<DeclAnnotation> = emptyList()
     ): ObjRecord {
         initClassScope()
         val existing = classScope!!.objects[name]
@@ -1021,6 +1065,7 @@ open class ObjClass(
             recordType = type,
             isTransient = isTransient,
             callSignature = callSignature,
+            annotations = annotations,
             fieldId = effectiveFieldId,
             methodId = effectiveMethodId
         )
@@ -1067,7 +1112,8 @@ open class ObjClass(
         isOverride: Boolean = false,
         pos: Pos = Pos.builtIn,
         prop: ObjProperty? = null,
-        methodId: Int? = null
+        methodId: Int? = null,
+        annotations: List<DeclAnnotation> = emptyList()
     ) {
         val g = getter?.let { ObjExternCallable.fromBridge { it() } }
         val s = setter?.let { ObjExternCallable.fromBridge { it(requiredArg(0)); ObjVoid } }
@@ -1076,7 +1122,8 @@ open class ObjClass(
             name, finalProp, false, visibility, writeVisibility, pos, declaringClass,
             isAbstract = isAbstract, isClosed = isClosed, isOverride = isOverride,
             type = ObjRecord.Type.Property,
-            methodId = methodId
+            methodId = methodId,
+            annotations = annotations
         )
     }
 

lynglib/src/commonMain/kotlin/net/sergeych/lyng/obj/ObjRecord.kt

@@ -16,6 +16,7 @@
  */
 
 package net.sergeych.lyng.obj
+import net.sergeych.lyng.DeclAnnotation
 import net.sergeych.lyng.Scope
 import net.sergeych.lyng.Visibility
 
@@ -40,6 +41,7 @@ data class ObjRecord(
     var receiver: Obj? = null,
     val callSignature: net.sergeych.lyng.CallSignature? = null,
     val typeDecl: net.sergeych.lyng.TypeDecl? = null,
+    val annotations: List<DeclAnnotation> = emptyList(),
     val memberName: String? = null,
     val fieldId: Int? = null,
     val methodId: Int? = null,

lynglib/src/commonTest/kotlin/net/sergeych/lyng/DeclAnnotationIntrospectionTest.kt

@@ -0,0 +1,68 @@
+/*
+ * Copyright 2026 Sergey S. Chernov real.sergeych@gmail.com
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package net.sergeych.lyng
+
+import kotlinx.coroutines.test.runTest
+import net.sergeych.lyng.obj.ObjInt
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+class DeclAnnotationIntrospectionTest {
+
+    @Test
+    fun classAnnotationQueriesExposeConstructorAndMemberAnnotations() = runTest {
+        val scope = Scope()
+        val result = scope.eval(
+            """
+            val suffix = "!"
+            
+            object Marker
+            
+            class Sample(
+                @Transient @Tag(1, label: "ctor", extra: suffix) val x: Int
+            ) {
+                @Transient @DbDecodeWith(Marker)
+                var y: Int = 10
+            }
+            
+            val ctorAnnotations: ImmutableList<Map<String, Object>> = Sample.getConstructorAnnotations("x")
+            val ctorTag: Map<String, Object> = ctorAnnotations[1]
+            val ctorPositional: ImmutableList<Object> = ctorTag["positional"] as ImmutableList<Object>
+            val ctorNamed: Map<String, Object> = ctorTag["named"] as Map<String, Object>
+            assertEquals(2, ctorAnnotations.size)
+            assertEquals("Transient", ctorAnnotations[0]["name"])
+            assertEquals("Tag", ctorTag["name"])
+            assertEquals(1, ctorPositional[0])
+            assertEquals("ctor", ctorNamed["label"])
+            assertEquals("!", ctorNamed["extra"])
+            
+            val memberAnnotations: ImmutableList<Map<String, Object>> = Sample.getMemberAnnotations("y")
+            val memberDecodeWith: Map<String, Object> = memberAnnotations[1]
+            val memberPositional: ImmutableList<Object> = memberDecodeWith["positional"] as ImmutableList<Object>
+            assertEquals(2, memberAnnotations.size)
+            assertEquals("Transient", memberAnnotations[0]["name"])
+            assertEquals("DbDecodeWith", memberDecodeWith["name"])
+            assertEquals(Marker, memberPositional[0])
+            
+            memberAnnotations.size + ctorAnnotations.size
+            """.trimIndent()
+        ) as ObjInt
+
+        assertEquals(4L, result.value)
+    }
+}

lynglib/stdlib/lyng/root.lyng

@@ -14,6 +14,24 @@ extern class NotImplementedException
 /* Raised when an awaited asynchronous task was cancelled before producing a value. */
 extern class CancellationException : Exception
 
+/* Runtime metaobject describing a class. */
+extern class Class {
+    /* Full name of this class including package if available. */
+    val className: String
+    /* Simple name of this class (without package). */
+    val name: String
+    /* Declared instance fields of this class and its ancestors (C3 order), without duplicates. */
+    val fields: List<String>
+    /* Declared instance methods of this class and its ancestors (C3 order), without duplicates. */
+    val methods: List<String>
+    /* Lookup a member by name in this class (including ancestors) and return it, or null if absent. */
+    fun get(name: String): Object?
+    /* Preserved annotations for a constructor parameter as descriptor maps with keys `name`, `positional`, and `named`. */
+    fun getConstructorAnnotations(name: String): ImmutableList<Map<String, Object>>
+    /* Preserved annotations for a member as descriptor maps with keys `name`, `positional`, and `named`. */
+    fun getMemberAnnotations(name: String): ImmutableList<Map<String, Object>>
+}
+
 /* A handle to a running asynchronous task. */
 extern class Deferred {
     /* Cancel the task if it is still active. Safe to call multiple times. */

notes/db/resultset_decode_api.md

@@ -0,0 +1,280 @@
+# ResultSet typed decode API
+
+Status: draft design note
+
+## Goal
+
+Extend `lyng.io.db` with row deserialization into ordinary Lyng objects using the new typed serialization-style API naming.
+
+Primary use case:
+
+```lyng
+class Point(x: Real, y: Real)
+
+val point = db.transaction { tx ->
+    tx.select(
+        "select row as x, col as y from data where not is_deleted"
+    ).decodeAs<Point>().first
+}
+```
+
+## Agreed API
+
+Use `decodeAs<T>()` as the only public API form in v1.
+
+Rationale:
+
+- matches the new typed serialization naming (`Json.decodeAs(...)`)
+- communicates decoding/materialization, not casting
+- keeps the common case strongly typed and chain-friendly
+- avoids adding a second runtime-type overload before it is needed
+
+Planned Lyng-facing declarations:
+
+```lyng
+extern class SqlRow {
+    fun decodeAs<T>(): T
+}
+
+extern class ResultSet : Iterable<SqlRow> {
+    fun decodeAs<T>(): Iterable<T>
+}
+```
+
+## Lifetime semantics
+
+`ResultSet.decodeAs<T>()` returns a transaction-scoped iterable view over the underlying result set.
+
+Rules:
+
+- the returned iterable must not be used after the owning transaction ends
+- decoded objects created during iteration are detached ordinary Lyng objects
+- to keep decoded values after the transaction, materialize them inside the transaction
+- normal materialization forms are `toList()`, `first`, `findFirst`, or manual iteration
+
+Valid:
+
+```lyng
+val points = db.transaction { tx ->
+    tx.select("select x, y from point")
+        .decodeAs<Point>()
+        .toList()
+}
+```
+
+Invalid:
+
+```lyng
+val decoded = db.transaction { tx ->
+    tx.select("select x, y from point").decodeAs<Point>()
+}
+
+decoded.first
+```
+
+## ResultSet shape
+
+`ResultSet.decodeAs<T>()` should preserve the current `ResultSet` paradigm:
+
+- `ResultSet` stays the row-producing source
+- `decodeAs<T>()` is a projection from `Iterable<SqlRow>` to `Iterable<T>`
+- no new DB-specific collection type is introduced in v1
+
+Implementation-wise, `ResultSet.decodeAs<T>()` can be defined as a lazy iterable that decodes each row via `SqlRow.decodeAs<T>()`.
+
+## Mapping discussion to finalize
+
+The following mapping behavior still needs explicit design decisions:
+
+- how constructor parameters are matched from columns
+- whether matching is case-insensitive
+- whether mutable serializable fields are populated after constructor call
+- treatment of default constructor values
+- treatment of nullable vs non-nullable targets
+- behavior for missing columns
+- behavior for extra columns
+- behavior for duplicate/ambiguous column labels
+- whether `onDeserialized()` is called after row decode
+- whether v1 supports only flat object decode or also nested shapes
+
+## Current direction for mapping
+
+Current likely direction, not finalized yet:
+
+- constructor parameters map by column label
+- matching is case-insensitive, consistent with `SqlRow["name"]`
+- after constructor call, remaining matching serializable mutable fields may be assigned
+- missing required non-null constructor values fail
+- missing nullable constructor parameters become `null`
+- defaulted constructor parameters use their defaults when the column is absent
+- ambiguous duplicate column labels fail
+- extra columns likely fail in strict mode for v1
+- `onDeserialized()` likely should run after the object is fully populated
+- v1 should likely stay flat and avoid nested/prefix-based mapping
+
+## Projection/conversion rules
+
+### General principle
+
+Row decoding should be strict and predictable.
+
+It should not globally treat every SQL string column as serialized JSON or every binary column as Lynon.
+
+That would be too implicit:
+
+- ordinary text columns are common and must stay ordinary text by default
+- ordinary binary/blob columns are common and must stay raw binary by default
+- automatic format decoding should happen only when there is a clear signal
+
+### Proposed conversion precedence
+
+For each constructor parameter or serializable mutable field:
+
+1. resolve the source column by name
+2. if the source value already matches the target type, use it directly
+3. if an explicit DB decoding attribute is present on the target member, apply that decoding rule
+4. otherwise, if the column metadata clearly indicates a special encoded DB type and the target is not the raw DB carrier type, apply the built-in format rule
+5. otherwise fail with a decode/type mismatch error
+
+### Direct match
+
+Direct match means the row value is already assignable to the target type after the normal SQL backend conversion.
+
+Examples:
+
+- SQL numeric column already surfaced as `Int`/`Real`/`Decimal`
+- SQL bool column surfaced as `Bool`
+- SQL date/time column surfaced as `Date`, `DateTime`, `Instant`
+- SQL text column surfaced as `String`
+- SQL binary column surfaced as `Buffer`
+
+These should not trigger any extra JSON/Lynon decoding.
+
+### Built-in encoded-column rules
+
+Current likely direction:
+
+- JSON/JSONB-like columns should decode through typed canonical `Json` when the target is not `String`
+- binary columns should decode through `Lynon` when the target is not `Buffer`
+
+This implies the current default:
+
+- string -> non-string is eligible for automatic typed `Json` decode only when the column metadata says the DB column is JSON-like
+- binary -> non-binary is decoded through `Lynon`
+- binary -> `Buffer` stays raw `Buffer`
+
+Examples:
+
+- PostgreSQL `json` / `jsonb` column into `Point` -> use typed `Json` decode
+- PostgreSQL `jsonb` column into `Map<String, Object?>` -> use typed `Json` decode
+- plain `text` / `varchar` column into `Point` -> fail unless explicitly annotated
+- `bytea` / `blob` column into `Buffer` -> direct match, no Lynon decode
+- `bytea` / `blob` column into `Point` -> decode with `Lynon`
+
+### Attribute-based explicit decoding
+
+Common explicit attributes look useful:
+
+- `@DbJson`
+- `@DbLynon`
+
+Applied to constructor parameters and serializable mutable fields.
+
+Meaning:
+
+- `@DbJson` means decode the column value as typed canonical JSON into the target member type
+- `@DbLynon` means decode the column value as Lynon into the target member type
+
+Example:
+
+```lyng
+class Record(
+    id: Int,
+    @DbJson payload: Payload,
+    @DbLynon cachedState: CacheEntry
+)
+```
+
+This keeps the common DB formats easy to use without making plain `String` or `Buffer` columns magical.
+
+Implementation note:
+
+- declaration metadata now preserves evaluated constructor-parameter and class-member annotation arguments
+- annotation arguments are evaluated once at declaration creation time and retained for the lifetime of the declaration
+- `@DbDecodeWith(...)` now uses that preserved metadata path
+
+### Generic custom decoder hook
+
+A generic hook is useful too, but it should be adapter-based, not lambda-based.
+
+Planned shape:
+
+- `@DbDecodeWith(adapter)`
+- `adapter` should be an instance of a dedicated interface such as `DbFieldAdapter`
+
+Reason:
+
+- a named adapter interface is easier to document and evolve than arbitrary callables
+- it gives us room for richer decoding context without baking ad-hoc callable signatures into annotations
+- it keeps the DB mapping API explicit and self-describing
+
+Current design direction:
+
+```lyng
+interface DbFieldAdapter {
+    fun decode(rawValue: Object?, column: SqlColumn, row: SqlRow, targetType: Object): Object? =
+        throw NotImplementedException("DB field adapter decode is not implemented")
+
+    fun encode(value: Object?, targetType: Object): Object? =
+        throw NotImplementedException("DB field adapter encode is not implemented")
+}
+```
+
+Decided:
+
+- `decode(...)` should receive the target type
+- adapters may be any ordinary instance, not only singleton objects
+- the same abstraction should later support symmetric `encode(...)`
+- adapter result must be checked against the target member type after decoding
+
+Still open before full implementation:
+
+- exact annotation shape for `@DbDecodeWith(...)`
+- whether target member name should also be passed
+- whether `targetType` should later get a more specific declaration type than plain `Object`
+
+Implemented in the current design:
+
+- `@DbDecodeWith(adapter)` on constructor parameters
+- `@DbDecodeWith(adapter)` on class-body fields/properties participating in `decodeAs<T>()`
+
+Future improvement:
+
+- compiler warning when preserved annotation metadata captures runtime state/closures
+- extend preserved annotation metadata beyond constructor parameters and class members to functions and top-level declarations
+
+### Arrays and maps
+
+Arrays and maps should not get DB-specific bespoke mapping in v1 unless they are coming through a recognized encoded format.
+
+Reason:
+
+- portable SQL array/map support is backend-specific and inconsistent
+- JSON columns already give us a portable representation for `List` and `Map`
+- adding DB-native array semantics now would complicate the contract too early
+
+So in v1:
+
+- if the backend already surfaces a value that directly matches the target type, use it
+- otherwise `List` / `Map` reconstruction should happen via `@DbJson` or recognized JSON-like column metadata
+
+### Recommended v1 policy
+
+Current recommended projection policy:
+
+- direct type match first
+- then explicit member attribute (`@DbJson`, `@DbLynon`)
+- then metadata-driven JSON decode for recognized JSON-like DB columns
+- then Lynon decode for binary columns when the target is not `Buffer`
+- no implicit JSON decode for arbitrary text columns
+- fail on anything else