What's New in Lyng 1.5 (vs 1.3.* / master)

This document summarizes the significant changes and new features introduced in the 1.5.0-SNAPSHOT development cycle.

Highlights

The return Statement: Added support for local and non-local returns using labels.
Abstract Classes and Interfaces: Full support for abstract members and the interface keyword.
Class Properties with Accessors: Define val and var properties with custom get() and set().
Restricted Setter Visibility: Use private set and protected set on fields and properties.
Late-initialized val: Support for val fields that are initialized in init blocks or class bodies.
Named Arguments and Splats: Improved call-site readability with name: value and map-based splats.
Refined Visibility: Improved protected access and closed modifier for better encapsulation.

Language Features

The `return` Statement

You can now exit from the innermost enclosing callable (function or lambda) using return. Lyng also supports non-local returns to outer scopes using labels.

fun findFirst<T>(list: Iterable<T>, predicate: (T)->Bool): T? {
    list.forEach {
        if (predicate(it)) return@findFirst it
    }
    null
}

Abstract Classes and Interfaces

Lyng now supports the abstract modifier for classes and their members. interface is introduced as a synonym for abstract class, allowing for rich multi-inheritance patterns.

interface Shape {
    abstract val area: Real
    fun describe() = "Area: %g"(area)
}

class Circle(val radius: Real) : Shape {
    override val area get = Math.PI * radius * radius
}

Class Properties with Accessors

Properties can now have custom getters and setters. They do not have automatic backing fields, making them perfect for computed values or delegation.

class Rectangle(var width: Real, var height: Real) {
    val area: Real get() = width * height
    
    var squareSize: Real
        get() = area
        set(v) {
            width = sqrt(v)
            height = width
        }
}

Named Arguments and Named Splats

Improve call-site clarity by specifying argument names. You can also expand a Map into named arguments using the splat operator.

fun configure(timeout: Int, retry: Int = 3) { ... }

configure(timeout: 5000, retry: 5)
val options = { timeout: 1000, retry: 1 }
configure(...options)

Modern Operators

The ?= operator allows for concise "assign if null" logic.

var cache: Map? = null
cache ?= { "status": "ok" } // Only assigns if cache is null

Tooling and IDE

IDEA Plugin: Significant improvements to autocompletion, documentation tooltips, and natural language support (Grazie integration).
CLI: The lyng fmt command is now a first-class tool for formatting code with various options like --check and --in-place.
Performance: Ongoing optimizations in the bytecode VM and compiler for faster execution and smaller footprint.

Migration Guide (from 1.3.*)

Check Visibility: Refined protected and private rules may catch previously undetected invalid accesses.
Override Keyword: Ensure all members that override ancestor declarations are marked with the override keyword (now mandatory).
Return in Shorthand: Remember that return is forbidden in = shorthand functions; use block syntax if you need early exit.

References

docs/OOP.md
docs/return_statement.md
docs/tutorial.md

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