FPC trunk has not been very friendly to existing code recently...

Today with r40792, the TAChart package fails to recompile: "tadiagram.pas(347,38) Error: Only static methods and static variables can be referenced through an object type". The faulty code is

     operator = (const A, B: TDiaPosition): Boolean;
     begin
       Result := TDiaPosition.Equals(A, B);
     end;

where

   operator =(const A, B: TDiaPosition): Boolean; overload; inline;

and

   type
      TDiaPosition = object
      public
       class function Equals(const A, B: TDiaPosition): Boolean;       ...

The last revision with which this line compiles is r40784. The next one, r40785, committed yesterday by Jonas ("give an error when trying to call an object instance method via a type node"), introduces the new issue.

What can I do to revive the package?

Am Mo., 7. Jan. 2019, 15:55 hat Werner Pamler
geschrieben:

Did you try to add "static" to the TDiaPosition.Equals class function? For an object type only instance and static class methods make sense so non static class methods should probably best be forbidden.

Regards,
Sven

True, reason is that *non* static means there is a Self. But since there is no "object of objecttype" and no "record of recordtype", there is no type for Self in class methods of objects/record.

Mattias

Sven Barth wrote

Did you try to add "static" to the TDiaPosition.Equals class function? For an object type only instance and static class methods make sense so non static class methods should probably best be forbidden.

That did the trick. Thank you.

But when only static class methods make sense why doesn't the compiler take this as default?

Mattias Gaertner wrote

True, reason is that *non* static means there is a Self. But since there is no "object of objecttype" and no "record of recordtype", there is no type for Self in class methods of objects/record.

Object class methods do have a self parameter. If an object has a vmt, the object class methods get this vmt pointer passed as self parameter. Otherwise they get nil as self parameter. Kylix does not support calling object class methods through tobjecttype.classmethod either, which is indeed kind of strange.

It is not possible to declare a non-static class method (in FPC, at least; Kylix does not support "advanced records", so I cannot test there).

Jonas

Thanks. I learned something new.

But what is this Self?

  TBird = object
    class procedure DoIt; virtual;
  end;
class procedure TBird.DoIt;
var
  o: TBird;
begin
  o:=Self;
  // Error: Incompatible types: got "Class Of TBird" expected "TBird"
end;

But "Class Of TBird" does not exist in FPC, does it?

It is not possible to declare a non-static class method (in FPC, at least; Kylix does not support "advanced records", so I cannot test there).

Mattias

No, it does not. The compiler currently unconditionally creates a classrefdef for the self parameter, regardless of whether it's a class or object type. This should probably changed into void pointer for objects. Although even Kylix prints "Error: Incompatible types: "TBird" and "Class Reference", so it seems we're also Delphi-compatible here :)

Jonas