Resolve the conflict

[LemonParty]

Is this problem can be resolved:

Code: Pascal  [Select][+][-]

1. {$mode objfpc}{$H+}
2. {$modeswitch advancedrecords}
3.  
4. type
5.   TRec1 = record
6.     D: DWord;
7.     class operator :=(constref R: TRec2): TRec1; {Identifier not found "TRec2"}
8.   end;
9.  
10.   TRec2 = record
11.     W: Word;
12.     class operator :=(constref R: TRec1): TRec2;
13.   end;
14.  
15.   class operator TRec1.:=(constref R: TRec2): TRec1;
16.   begin
17.                
18.   end;
19.  
20.   class operator TRec2.:=(constref R: TRec1): TRec2;
21.   begin
22.                
23.   end;
24.  
25. begin
26.  
27. end.
28.  

[Josh]

Code: Pascal  [Select][+][-]

1.  TRec1 = record
2.     D: DWord;
3.     class operator :=(constref R: TRec2): TRec1; {Identifier not found "TRec2"}
4.   end;

your using trec2 which is not defined yet.

maybe something like

Code: Pascal  [Select][+][-]

1. type
2.   TRec1 = record
3.     D: DWord;
4.   end;
5.  
6.   TRec2 = record
7.     W: Word;
8.   end;
9.  
10. class operator TRec1.:=(constref R: TRec2): TRec1;
11. begin
12.  
13. end;
14.  
15. class operator TRec2.:=(constref R: TRec1): TRec2;
16. begin
17.  
18. end;
19.  

[Warfley]

Unlike languages like C, Pascal does not support forward type Declarations for non pointer (and class) types

So short answer: Thats simply not possible if you need to use class operators

[440bx]

That brings the possibility of using pointers to records instead of the record types.

if he used PRec2 instead of TRec2, he could make it work but, it also means the operator applies directly to a pointer type instead of indirectly by using constref.

[LemonParty]

Thats simply not possible if you need to use class operators

This is limit a feature usage. Very bad.

[runewalsh]

Operators can be defined as free functions.

Code: Pascal  [Select][+][-]

1. {$mode objfpc}{$H+}
2. type
3.         TRec1 = record
4.                 D: DWord;
5.         end;
6.  
7.         TRec2 = record
8.                 W: Word;
9.         end;
10.  
11.         operator :=(const R: TRec2): TRec1;
12.         begin
13.         end;
14.  
15.         operator :=(const R: TRec1): TRec2;
16.         begin
17.         end;
18.  
19. begin
20. end.

[ALLIGATOR]

This can be done and it works in Delphi12.1CE, but does not work in FPC [main] :

Code: Pascal  [Select][+][-]

1. program kek;
2. {$ifdef FPC}{$mode delphi}{$endif}
3.  
4. type
5.   TRec1 = record
6.   end;
7.   TRec2 = record
8.     class operator Explicit(const R: TRec1): TRec2;
9.   end;
10.   TRec1Helper = record helper for TRec1
11.     class operator Explicit(const R: TRec2): TRec1;
12.   end;
13.  
14. class operator TRec1Helper.Explicit(const R: TRec2): TRec1;
15. begin
16. end;
17.  
18. class operator TRec2.Explicit(const R: TRec1): TRec2;
19. begin
20. end;
21.  
22. begin
23. end.

FPC [main]: FAIL ❌😵
D12.1CE: OK ✅😇

Found an issue on this topic:
https://gitlab.com/freepascal.org/fpc/source/-/issues/40788

[AlexK]

Unlike languages like C, Pascal does not support forward type Declarations for non pointer (and class) types

So short answer: Thats simply not possible if you need to use class operators

Let it be explicit pointers then.

Code: Pascal  [Select][+][-]

1. type
2.   PRec1 = ^TRec1;
3.   PRec2 = ^TRec2;
4.  
5.   TRec1 = record
6.     D: DWord;
7.     class operator := (const R: PRec2): TRec1;
8.   end;
9.  
10.   TRec2 = record
11.     W: word;
12.     class operator := (const R: PRec1): TRec2;
13.   end;
14.  
15.   class operator TRec1.:=(const R: PRec2): TRec1;
16.   begin
17.  
18.   end;
19.  
20.   class operator TRec2.:=(const R: PRec1): TRec2;
21.   begin
22.  
23.   end;
24.  
25. begin
26. end.    
27.  

2013, https://gitlab.com/freepascal.org/fpc/source/-/issues/24425 :

Adding extensions that can only be used in very specific scenarios complicate the language (because the programmer has to think about the fact where it can be used and not) and the compiler (it has to add checks for all of these cases), and are generally not a good idea.

[Thaddy]

But warn: in the above the records are of different size, so would need quite some extra logic inside the operators.
You can't simply write

Code: Pascal  [Select][+][-]

1.   class operator TRec1.:=(constref R: PRec2): TRec1;
2.   begin
3.      move(R^,Result,SizeOf(Result)); // only possible if size of the records are equal        
4.   end;

This is only possible if the records are the same size.