Using attributes on aliases

[havrlisan 3]

Is it possible to use attributes in these scenarios:

// First scenario
[MyAttr]
TMyGuid = TGuid;

// Second scenario
[MyAttr]
TMyDT = TDateTime;

I found this article that says it's not possible to use attributes on aliases of simple ordinal types, only on actual sub-types by using the type keyword. I'm asking this because I believe declaring my TMyGuid type as a sub-type for TGuid rather than an alias will break a lot of my code. Is there really no way to use attributes on aliases like this?

 

Update: I realized that changing my declaration to

TMyGuid = type TGuid;

will only cause the loss of TGuidHelper. Unfortunately, class helper inheritance is still not available so I will have to rewrite it for my sub-type.

Edited December 9, 2022 by havrlisan
update

[programmerdelphi2k 235]

type
  TMyGUID = TGUID; // your "alias" that way

  TMyHlpToTGUID = record helper for TGUID
    function MyFunc: string;
  end;

  TMyHlpToTMyGUID = record helper for TMyGUID
    function MyMyFunc: string;
  end;

procedure TForm1.Button1Click(Sender: TObject);
var
  x: TMyGUID;
begin
  x := TMyGUID.Create('123...');
  x.MyMyFunc; // MyMyFunc "hide" MyFunc now... helper to same type-base TGUID!
end;

{ TMyHlpToTGUID }

function TMyHlpToTGUID.MyFunc: string;
begin
  result := 'Hello';
end;

{ TMyHlpToTMyGUID }

function TMyHlpToTMyGUID.MyMyFunc: string;
begin
  result := 'World';
end;

end.

as "TMyGUID" is, in fact, "TGUID" (yet), then your attributes should works in "TGUID" not in "TMyGUID"

as showed in your "blog post", the real type is "TGUID", then, you needs works with it, not "TMyGUID"

 

Edited December 9, 2022 by programmerdelphi2k

[havrlisan 3]

On 12/9/2022 at 2:11 PM, programmerdelphi2k said:

type
  TMyGUID = TGUID; // your "alias" that way

  TMyHlpToTGUID = record helper for TGUID
    function MyFunc: string;
  end;

  TMyHlpToTMyGUID = record helper for TMyGUID
    function MyMyFunc: string;
  end;

procedure TForm1.Button1Click(Sender: TObject);
var
  x: TMyGUID;
begin
  x := TMyGUID.Create('123...');
  x.MyMyFunc; // MyMyFunc "hide" MyFunc now... helper to same type-base TGUID!
end;

{ TMyHlpToTGUID }

function TMyHlpToTGUID.MyFunc: string;
begin
  result := 'Hello';
end;

{ TMyHlpToTMyGUID }

function TMyHlpToTMyGUID.MyMyFunc: string;
begin
  result := 'World';
end;

end.

as "TMyGUID" is, in fact, "TGUID" (yet), then your attributes should works in "TGUID" not in "TMyGUID"

as showed in your "blog post", the real type is "TGUID", then, you needs works with it, not "TMyGUID"

 

I see, so it is not possible to declare attributes for aliases. Thanks for your answer.