From 9aae33d56402661913b1630b13127bf13dbb1f96 Mon Sep 17 00:00:00 2001
From: sergeych <real.sergeych@gmail.com>
Date: Fri, 8 Aug 2025 19:33:17 +0300
Subject: [PATCH] fix #48 flows

---
 docs/parallelism.md                            | 15 ++++++++++++---
 .../kotlin/net/sergeych/lyng/obj/ObjFlow.kt    |  4 ----
 .../src/commonTest/kotlin/CoroutinesTest.kt    | 18 +++++-------------
 3 files changed, 17 insertions(+), 20 deletions(-)

diff --git a/docs/parallelism.md b/docs/parallelism.md
index c1f0c0e..ab14c8c 100644
--- a/docs/parallelism.md
+++ b/docs/parallelism.md
@@ -160,23 +160,32 @@ Great: the generator is not executed until collected bu the `f.take()` call, whi
 
 Important difference from the channels or like, every time you collect the flow, you collect it anew:
 
+    var isStarted = false
     val f = flow {
             emit("start")
+            isStarted = true
             (1..4).forEach { emit(it) }
     }
+    // flow is not yet started, e.g. not got execited, 
+    // that is called 'cold':
+    assertEquals( false, isStarted )
+
     // let's collect flow:
     val result = []
     for( x in f ) result += x
     println(result)
 
-    // let's collect it once again:
+    assertEquals( true, isStarted)
+
+    // let's collect it once again, it should be the same:
     println(f.toList())
 
     // and again:
-    //assertEquals( result, f.toList() )
+    assertEquals( result, f.toList() )
 
     >>> ["start", 1, 2, 3, 4]
     >>> ["start", 1, 2, 3, 4]
     >>> void
 
-1
+Notice that flow's lambda is not called until actual collection is started. Cold flows are
+better in terms of resource consumption.
diff --git a/lynglib/src/commonMain/kotlin/net/sergeych/lyng/obj/ObjFlow.kt b/lynglib/src/commonMain/kotlin/net/sergeych/lyng/obj/ObjFlow.kt
index 6707214..c05d062 100644
--- a/lynglib/src/commonMain/kotlin/net/sergeych/lyng/obj/ObjFlow.kt
+++ b/lynglib/src/commonMain/kotlin/net/sergeych/lyng/obj/ObjFlow.kt
@@ -23,10 +23,7 @@ class ObjFlowBuilder(val output: SendChannel<Obj>) : Obj() {
         val type = object : ObjClass("FlowBuilder") {}.apply {
             addFn("emit") {
                 val data = requireOnlyArg<Obj>()
-                println("well well $data")
                 try {
-                    println("builder ${thisAs<ObjFlowBuilder>().hashCode()}")
-                    println("channel ${thisAs<ObjFlowBuilder>().output.hashCode()}")
                     val channel = thisAs<ObjFlowBuilder>().output
                     if( !channel.isClosedForSend )
                         channel.send(data)
@@ -74,7 +71,6 @@ class ObjFlow(val producer: Statement) : Obj() {
             }
         }.apply {
             addFn("iterator") {
-                println("called iterator!")
                 ObjFlowIterator(thisAs<ObjFlow>().producer)
             }
         }
diff --git a/lynglib/src/commonTest/kotlin/CoroutinesTest.kt b/lynglib/src/commonTest/kotlin/CoroutinesTest.kt
index d149878..d1c951a 100644
--- a/lynglib/src/commonTest/kotlin/CoroutinesTest.kt
+++ b/lynglib/src/commonTest/kotlin/CoroutinesTest.kt
@@ -90,28 +90,20 @@ class TestCoroutines {
     fun testFlow2() = runTest {
         eval("""
                 val f = flow {
-                    println("Starting generator")
                         emit("start")
                         emit("start2")
-                        println("Emitting")
                         (1..4).forEach { 
-//                            println("you hoo "+it)
                             emit(it) 
                         }
-                        println("Done emitting")
                 }
                 // let's collect flow:
                 val result = []
-//                for( x in f ) result += x
-                println(result)
-            
+                for( x in f ) result += x
+                    println(result)
+                
                 // let's collect it once again:
-                println(f.toList())
-                println(f.toList())
-//                for( x in f ) println(x)
-//                for( x in f ) println(x)
-            
-                //assertEquals( result, f.toList() )
+                assertEquals( result, f.toList())
+                assertEquals( result, f.toList())
         """.trimIndent())
     }
 }
\ No newline at end of file