Lazarus

Programming => General => Topic started by: JdeHaan on July 03, 2022, 12:04:22 pm

Title: Type helper for TArray<T>
Post by: JdeHaan on July 03, 2022, 12:04:22 pm

Hi,

I'm trying to extend TArray<T> generic with some functions and procedures, however, I can't get it to compile. Errors are in the code below. I'm not sure if it's possible what I want: to extend a generic with a generic type helper, or that I'm just messing it up. Pls give me some direction.

Code: Pascal  [Select][+][-]

1. unit uArray;
2.  
3. {$mode delphi}{$H+}
4. {$ModeSwitch typehelpers}
5.  
6. interface
7.  
8. uses
9.   SysUtils;
10.  
11. type
12.  
13.   TArray<T> = array of T;
14.  
15.   TArrayHelper<T> = type helper for TArray<T>
16.     procedure InsertRange(const Index: Integer; Values: TArray<T>);
17.   end;
18.  
19. implementation
20.  
21. { TArrayHelper }
22.  
23. procedure TArrayHelper<T>.InsertRange(const Index: Integer; Values: TArray<T>);
24. begin
25.   // insert the range
26. end;
27.  
28. end.
29.  
30. {
31. 4 errors on line 15
32.  
33. Error: Syntax error "indentifier expected, but "<" found
34. Error: Type identifier expected
35. Error: Generics without specialization cannot be used as a type for a variable
36.  
37. [15,44] Error: expected ., but T found
38. }
39.  

Lazarus v 2.3.0 (date 2022-05-27); FPC v 3.3.1 (x86-64 Darwin Cocoa)

Title: Re: Type helper for TArray<T>
Post by: Thaddy on July 03, 2022, 02:10:09 pm

TArray<T> is already in system, so that may clash with a re-declaration.
E.g. this small example unit:

Code: Pascal  [Select][+][-]

1. unit naamloosunit;
2. {$mode delphi}
3. interface
4. type
5.    TspecializeMeToInteger = TArray<Integer>;
6. implementation
7. end.

Title: Re: Type helper for TArray<T>
Post by: PascalDragon on July 03, 2022, 02:14:05 pm

Quote from: JdeHaan on July 03, 2022, 12:04:22 pm

I'm trying to extend TArray<T> generic with some functions and procedures, however, I can't get it to compile. Errors are in the code below. I'm not sure if it's possible what I want: to extend a generic with a generic type helper, or that I'm just messing it up. Pls give me some direction.

Generic type helpers are currently not supported.

Quote from: Thaddy on July 03, 2022, 02:10:09 pm

TArray<T> is already in system, so that may clash with a re-declaration.

Redeclarations are never a problem, units are namespaces after all. Having both units in the same scope however might lead to confusion (though dynamic arrays are handled a bit special here).

Title: Re: Type helper for TArray<T>
Post by: JdeHaan on July 03, 2022, 02:47:51 pm

Quote

Generic type helpers are currently not supported.

@PascalDragon, thanks. It would be a nice feature...

Title: Re: Type helper for TArray<T>
Post by: PascalDragon on July 04, 2022, 01:55:11 pm

Quote from: JdeHaan on July 03, 2022, 02:47:51 pm

Quote

Generic type helpers are currently not supported.

@PascalDragon, thanks. It would be a nice feature...

Support for generic type helpers is on my ToDo list, but even if they're implemented you would still need to specialize the type helper for your final type, because the compiler can't do implicit specializations for types.