gistfile1.hx

abstract FunctionReturning<T>(Dynamic) {
  inline function new (x:Dynamic) this = x;
  @:from static inline function from0 <T>(x:Void->T):FunctionReturning<T> return new FunctionReturning(x);
  @:from static inline function from1 <T>(x:Dynamic->T):FunctionReturning<T> return new FunctionReturning(x);
  @:from static inline function from2 <T>(x:Dynamic->Dynamic->T):FunctionReturning<T> return new FunctionReturning(x);
  @:from static inline function from3 <T>(x:Dynamic->Dynamic->Dynamic->T):FunctionReturning<T> return new FunctionReturning(x);
  /* ... */
}

class Test {

  public static function expectReturningInt (x:FunctionReturning<Int>) {
	
  }
  public static function main () {
	expectReturningInt(function () return 1); // works
	expectReturningInt(function (z:String) return 1); // works
	expectReturningInt(function (z:String) return "hi"); // compile time error
  }
}