Arithmetic operations with generic types in Delphi

Question

I\'m new in Delphi. For a project required by my company, I need to translate some code from our existing C++ classes to Delphi. Some of these classes are templates, such as

Answer 1

Pointing this out for anyone else looking for an Object Pascal solution to this general issue:

Note that Free Pascal quite simply does support exactly what they're trying to do here (even in "Delphi-syntax compatibility" mode.)

As someone who had only used Free Pascal for a long time, I was honestly very surprised that Delphi doesn't allow this at all, once I realized that was the case. It's a significant limitation IMO.

Valid Free Pascal code:

program Example;

// Using Delphi-mode here allows us to declare and use
// generics with the same syntax as Delphi, as opposed to
// needing the "generic" and "specialize" keywords that
// FPC normally requires.

{$mode Delphi}

// To allow +=, another nice FPC feature...

{$COperators On}

type
  TGPoint = record
    X, Y: T;
    // static class function instead of constructor here so we can inline it
    class function Create(constref AX, AY: T): TGPoint; static; inline;
    // define our operator overload
    class operator Add(constref Left, Right: TGPoint): TGPoint; inline;
  end;

  class function TGPoint.Create(constref AX, AY: T): TGPoint;
  begin
    with Result do begin
      X := AX;
      Y := AY;
    end;
  end;

  class operator TGPoint.Add(constref Left, Right: TGPoint): TGPoint;
  begin
    with Result do begin
      X := Left.X + Right.X;
      Y := Left.Y + Right.Y;
    end;
  end;

var SP: TGPoint;

begin
  SP := TGPoint.Create('Hello, ', 'Hello, ');
  SP += TGPoint.Create('world!', 'world!');
  with SP do begin
    WriteLn(X);
    WriteLn(Y);
  end;
end.

The program of course prints:

Hello, world!
Hello, world!