Haxe - mapping a string to a class

Question

How should I go about mapping a string to a class in Haxe, and then instantiating it?

class Foo{}
class Bar extends Foo{}
class Buzz extends Foo{}

// (...)

var classMap:Map<String, Class<Foo>> = [
    "abc" => Bar,
    "def" => Buzz
];
var myClass:Class<Foo> = classMap["abc"];
var myObj:Foo = new myClass(/* params */);

I thought this would work, but it throws unexpected ( after myClass. What's wrong?

Answer 1

Instead of storing Class<T> in the map and resorting to reflection for instantiation, it's a much nicer pattern to store references to the constructors (using their function type) as detailed in this haxe.org blog post.

class Foo {}
class Bar extends Foo {
    public function new() {}
}
class Buzz extends Foo {
    public function new() {}
}

var constructors:Map<String, Void->Foo> = [
    "abc" => Bar.new,
    "def" => Buzz.new
];
var construct:Void->Foo = constructors["abc"];
var myObj:Foo = construct();

https://try.haxe.org/#49E93

Unlike the Type.createInstance() approach, this doesn't allow you to pass arbitrary arguments to the constructors they might not even accept, so it's much more type-safe. It also automatically works with dead code elimination because Haxe sees that the constructors are referenced.

Answer 2

You should use Type.createInstance to create an instance of that class. new will only work if you want to directly call the constructor on the Class name itself new Foo()

I suggest you do it this way:

var myClass:Class<Foo> = classMap["abc"];
var myObj:Foo = Type.createInstance(myClass, [/* params */]);

Try it online here: https://try.haxe.org/#3134A