Pointer in Generics

[Okoba]

Hello,

Why the "TPointer<T> = ^T;" raises an error? And what is the correct way?
Also when I write "TPointer<T> = ^T;", FPC raise the error at line of Test1, and it most probably is a bug.

Code: Pascal  [Select][+][-]

1. program Project1;
2.  
3. {$mode delphi}
4.  
5. type
6.   TArray<T> = array of T;
7.   TPointer<T> = ^T;
8.  
9.   procedure Test1<T>(A: TArray<T>);
10.   begin
11.  
12.   end;
13.  
14.   procedure Test2<T>(A: TPointer<T>);
15.   begin
16.  
17.   end;
18.  
19. begin
20. end.                          

[PascalDragon]

Why the "TPointer<T> = ^T;" raises an error? And what is the correct way?

Generic pointers are not supported. (Though I am playing with the tought to support them considering that arrays are supported as well).

As a workaround you can use a type inside a generic record:

Code: Pascal  [Select][+][-]

1. {$mode delphi}
2. {$modeswitch advancedrecords}
3.  
4. type
5.   TPointer<T> = record
6.   type
7.     PT = ^T;
8.   end;
9.  
10. procedure Test1<T>(A: TPointer<T>.PT);
11. begin
12.   Writeln(HexStr(A));
13. end;
14.  
15. var
16.   l: LongInt;
17.   p: PLongInt;
18. begin
19.   p := @l;
20.   Test1<LongInt>(p);
21. end.

Also when I write "TPointer<T> = ^T;", FPC raise the error at line of Test1, and it most probably is a bug.

Please report that as a bug.

[Okoba]

Thank you. Is there an issue for Generic pointers so I can subscribe too?

[Okoba]

Trying your solution more in a unit, there is a problem:

Code: Pascal  [Select][+][-]

1. program Project1;
2.  
3. {$mode delphi}
4. {$modeswitch advancedrecords}
5.  
6. uses unit1;
7.  
8. begin
9.   p := @l;
10.   Test1<Longint>(p);
11. end.          

Code: Pascal  [Select][+][-]

1. unit Unit1;
2.  
3. {$mode delphi}
4. {$modeswitch advancedrecords}
5.  
6. interface
7.  
8. type
9.   TPointer<T> = record
10.   type
11.     PT = ^T;
12.   end;
13.  
14. procedure Test1<T>(A: TPointer<T>.PT);
15.  
16. implementation
17.  
18. procedure Test1<T>(A: TPointer<T>.PT); //unit1.pas(18,11) Error: Function header doesn't match the previous declaration "Test1$1(TPointer$1$crcBAA2E09C_crcBD58B68D.PT);"
19. begin
20.   Writeln(HexStr(A));
21. end;
22.  
23. end.                                                                                                            

Why?

[PascalDragon]

Thank you. Is there an issue for Generic pointers so I can subscribe too?

No, there is not.

Why?

Hmm... bug... please report.

[Okoba]

Reported as #40090 and #40091.

[PascalDragon]

Thank you.