wing-immutable

Make a variable immutable.
Raise a runtime error on reassignment.

Normally if it is final field, it must be assigned in the constructor.
The purpose is to allow the first assignment in other functions.

Usage

import wing.Immutable;

class Foo {
	final foo:Immutable<Bool> = new Immutable();

	public function new() {
		setup();
	}
	
	function setup():Void {
		// The first assignment is OK.
		foo.assign(true);
		// By `@:forward` metadata, can be used like the underlying type.
		trace(foo == true);
		
		// After the second time, runtime error.
		foo.assign(false);
	}
}

Tips: When public, prevent assignment from outside the class

final _foo:Immutable<Bool> = new Immutable();
public var foo(get, never):Null<Bool>;
inline function get_foo():Null<Bool> {
	return _foo;
}

or

final foo:Immutable<Bool> = new Immutable();
public inline function getFoo():Null<Bool> {
	return foo;
}