Overload Add statement for three extended entries

Question

Delphi 2006 introduced operator overloading, which was later fixed in Delphi 2007. This applies to Delphi 2007.

Why the following does not compile:

type
  TFirstRec = record
    // some stuff
  end;

type
  TSecondRec = record
    // some stuff
  end;

type
  TThirdRec = record
    // some stuff
    class operator Add(_a: TFirstRec; _b: TSecondRec): TThirdRec;
end;

class operator TThirdRec.Add(_a: TFirstRec; _b: TSecondRec): TThirdRec;
begin
   // code to initialize Result from the values of _a and _b
end;

var
  a: TFirstRec;
  b: TSecondRec;
  c: TThirdRec;
begin
  // initialize a and b

  c := a + b; // <== compile error: "Operator not applicable to this operand type"
end.

Since I declared a statement that adds two operands a of type TFirstRec and b of type TSecondRec, which results in TThirdRec, I would expect this to compile.

(If you need something less abstract, think about TMyDate, TMyTime, and TMyDateTime.)

Answer 1

When I tried to compile code in Delphi 2009, I got a compiler error

[ Pascal] Project1.dpr(21): E2518 "" "TThirdRec"

class operator Add(_a: TFirstRec; _b: TSecondRec): TThirdRec;

- , (_a; _b) TThirdRec

Answer 2

. :

program Project51;

{$APPTYPE CONSOLE}

uses
  SysUtils;

type
  TThirdRec = record
    // some stuff
  end;

  TFirstRec = record
    // some stuff
  end;

  TSecondRec = record
    // some stuff
    class operator Add(_a: TFirstRec; _b: TSecondRec): TThirdRec;
  end;

class operator TSecondRec.Add(_a: TFirstRec; _b: TSecondRec): TThirdRec;
begin
   // code to initialize Result from the values of _a and _b
end;

var
  a: TFirstRec;
  b: TSecondRec;
  c: TThirdRec;
begin
  // initialize a and b

  c := a + b; // <== compile error: "Operator not applicable to this operand type"
end.

, "" TFirstRec, TSecondRec TThirdRec, Delphi .