Immutable

A Haxe 4 library for making your local vars immutable with

haxelib install immutable

-lib immutable

class YourClass implements Immutable
{
	// For immutable class fields, use the Haxe 4 "final" keyword.
	public final test : String;

	public function new() {
		test = "Final";
	}

	public function test() {
		var a = 123;
		a = 234; // *** Compilation error

		@mutable var b = 123;
		b = 234; // Ok
	}

	public function test2(a : String, @mutable b : Int) {
		a = "changed"; // *** Compilation error
		b = 123; // Ok
	}
}

Since the library is enforcing this at compile-time, it won't slow down your code. It may affect compilation time a little, so in certain cases you may choose to disable all checking with -D disable-immutable.

ES6-style

When implementing Immutable, vars will behave like const and let, used in modern javascript:

Limitations

No type information

If the compiler cannot find any type information, it cannot make the var immutable and will fail compilation. The library does its best to alleviate this, but if it fails the way to fix it is to provide the type yourself:

var a = [1,2,3,4]; // No problem, type inferred.

var b = a.something(...); // Could fail compilation, no type information found.

var c : Array<Int> = a.something(...); // No problem, type hint used.

Short lambdas

They are made to be short, so providing type information isn't convenient in this case. Therefore, if an unnamed function is returning as its first expression, it's considered to be a lambda and the arguments will be mutable. You can define immutable vars inside the function as usual.

Problems?

Please open an issue if you happened to trick the library, or if you think something is conceptually or semantically wrong. Using Reflect isn't tricking though, it's intentional!