Unify structure with one that requires more fields if all of them are read only and optional.

[back2dos]

Basically I would like this to compile:

class Test {
  static function main() {
    var l:Less = { foo: 42 };
    var m:More = l;
  }
}

typedef Less = {
  var foo(default, never):Int;
}
    
typedef More = {
  @:optional var foo(default, never):Int;
  @:optional var bar(default, never):Int;    
}

The compiler tells me Less should be More but I would argue that in this case Less indeed is More ;)

[Simn]

If I recall correctly, @ousado has shown that this is not sound.

[back2dos]

Upon second though I realize now that this requires special treatment on some static targets when the object is actually an instance. Right now it can just blow up: http://try.haxe.org/#Fd4A1 - that said, an additional check could be performed before accessing @:optional fields through anonymous types. That makes this a bigger deal than I initially though, but short of a counter example I still think it would be a good idea to add eventually.

[ousado]

Yes, it's not sound - the following would compile:

class Test {
  static function main() {
    var m2:More2 = {foo:1,bar:"2"};
    var l:Less = m2;
    var m:More = l;
  }
}

typedef Less = {
  var foo(default, never):Int;
}
    
typedef More = {
  @:optional var foo(default, never):Int;
  @:optional var bar(default, never):Int;    
}
typedef More2 = {
  var foo(default, never):Int;
  var bar(default, never):String;    
}

[back2dos]

Well, I suppose it's generally a fair question whether More2 and More should unify only in one direction (going from non-optional to optional) in the first place, but I see now that my request would require quite a few changes on anonymous types. Thanks for the info ;)