Type Traits

Traits.hx

typedef MapApi<K,V> = {
   public function set(key:K,value:V) : Void;
   public function get(key:K) : Null<V>;
};

@:generic
extern abstract Checker<Typedef, Instance:Typedef> (Dynamic)
{
   static var instance:Instance;
   inline public function new() { this = null; }
}

// Works - no Api check
typedef MyMap<K:Int,V> =  haxe.ds.IntMap<V>;
// Can't have both active, although they are mutualy exclusive
//typedef MyMap<K:String,V> =  haxe.ds.StringMap<V>;
//typedef MyMap<K:{},V> =  haxe.ds.ObjectMap<V>;


// Api check works after the fact
typedef Check1 = Checker< MapApi<Int,Int>, MyMap<Int,Int> >;
// Fails as desired
//typedef Check2 = Checker< MapApi<Int,Int>, MyMap<Int,String> >;


// Allow combination:

// expose internal types?
//typedef MyMap<K:Int,V> =  Checker< MapApi<Int,Int>, MyMap<Int,Int> >.Instance;
// or some macro exists today ?
//typedef MyMap<K:Int,V> =  Tool.typeof( Checker< MapApi<Int,Int>, MyMap<Int,Int> >.instance );

class Traits
{
   public static function main()
   {
      var t = new MyMap<Int,String>();
      t.set(1,"a");
      trace(t.get(1));
   }
}

This shows how apis can be checked without inheritance. Allowing multiple typedefs, and selecting the best one allows completely different implementations to be used. With a little syntactic sugar or some macro magic, the type may be defined and checked at compile-time, with zero visibility at run-time.