instance IndexGet Map[K,V] K {
	function index_get(self:ref Map[K,V], key:ref K):ref V{
		....
	}
}

instance IndexSet Map[K,V] K V {
	function index_set(self:ref Map[K,V], key:ref K, value:ref V){
		....
	}
}


var m:Map[i32, i64] = ...;

m[1] = 2; //index_set(&m, &1, &2);
var x:i64 = m[1]; //*index_get(&m, &1);