Lazarus

Programming => General => Topic started by: bpranoto on March 26, 2023, 12:21:28 pm

Title: Generic: array of T
Post by: bpranoto on March 26, 2023, 12:21:28 pm

Why is it not compiled?

Code: Pascal  [Select][+][-]

1. program Project1;
2. uses sysutils;
3.  
4. var
5.   ATanggal:array of TDate;
6.  
7. generic procedure ArrayAdd<T>( var A:array of T ; Item:T);
8. var
9.   i:Integer;
10. begin
11.   i := Length(A);
12.   SetLength(A,i+1);  // <=== Error: type mismatch
13.   A[i]:=item;
14. end;
15.  
16. begin
17.   SetLength(ATanggal,0);
18.   specialize ArrayAdd<TDate>( ATanggal, Date);
19. end.
20.  

Title: Re: Generic: array of T
Post by: Thaddy on March 26, 2023, 12:33:48 pm

Because, again, many people do that, you are mixing up  open array parameters with dynamic arrays.
The correct way is something like this:

Code: Pascal  [Select][+][-]

1. {$mode objfpc}{$H+}
2. uses sysutils;
3.  
4. var
5.   ATanggal:array of TDate;
6.  
7. generic procedure ArrayAdd<T>( var A:specialize TArray<T> ; Item:T); // take a good look!!
8. var
9.   i:Integer;
10. begin
11.   i := Length(A);
12.   SetLength(A,i+1);  // <=== No Error
13.   A[i]:=item;
14. end;
15.  
16. begin
17.   SetLength(ATanggal,0);
18.   specialize ArrayAdd<TDate>( ATanggal, Date);
19. end.

There's more wrong, but the above is close to your code and works. At least with trunk. Can't test other versions today.

Title: Re: Generic: array of T
Post by: bpranoto on March 26, 2023, 12:39:20 pm

Thank you for the enlightment.

Title: Re: Generic: array of T
Post by: bpranoto on March 26, 2023, 03:05:59 pm

Quote from: Thaddy on March 26, 2023, 12:33:48 pm

There's more wrong, but the above is close to your code and works. At least with trunk. Can't test other versions today.

it works with fpc 3.2.2