Generic records with variable array size (generics with types and numerics)

[Fibonacci]

What I want to achieve is something like this: to create a generic record and specialize it with a specific number of elements in its array.

Code: Pascal  [Select][+][-]

1. type
2.   generic tgenrec<T, N> = record
3.     data: array[0..N-1] of T;
4.   end;
5.  
6. var
7.   myrec100: specialize tgenrec<dword, 100>; // project1.lpr(7,43) Error: Error in type definition
8.   myrec500: specialize tgenrec<dword, 500>; // project1.lpr(8,43) Error: Error in type definition
9.  
10. begin
11. end.

Maybe this is possible, only I dont know about it

I managed to come up with a little hack to achieve something that kind of does the job, but is limited to a having a predefined array of bytes due to the use of SizeOf().

Code: Pascal  [Select][+][-]

1. type
2.   arr100    = array[1..100]    of byte;
3.   arr500    = array[1..500]    of byte;
4.   arr1000   = array[1..1000]   of byte;
5.   arr50000  = array[1..50000]  of byte;
6.   arr275000 = array[1..275000] of byte;  
7.  
8.   generic tgenrec<T, N> = record
9.     data: array[0..sizeof(N)-1] of T;
10.   end;
11.  
12. var
13.   myrec100: specialize tgenrec<byte, arr100>;
14.   myrec500: specialize tgenrec<byte, arr500>;
15.  
16. begin
17.   writeln('sizeof myrec100 = ', sizeof(myrec100));
18.   writeln('sizeof myrec500 = ', sizeof(myrec500));
19.   writeln;
20.  
21.   writeln('sizeof custom genrec = ', sizeof( specialize tgenrec<byte, arr100>    ));
22.   writeln('sizeof custom genrec = ', sizeof( specialize tgenrec<byte, arr500>    ));
23.   writeln('sizeof custom genrec = ', sizeof( specialize tgenrec<byte, arr1000>   ));
24.   writeln('sizeof custom genrec = ', sizeof( specialize tgenrec<byte, arr50000>  ));
25.   writeln('sizeof custom genrec = ', sizeof( specialize tgenrec<byte, arr275000> ));
26.  
27.   readln;
28. end.

What do you guys think about it? Anyone know a better solution?

EDIT: One thing I should mention, I cant use dynamic arrays and SetLength()

[PascalDragon]

What do you guys think about it? Anyone know a better solution?

In main constant parameters are supported:

Code: Pascal  [Select][+][-]

1. program tgenconst;
2.  
3. type
4.   generic tgenrec<T; const N: SizeInt> = record
5.     data: array[0..N-1] of T;
6.   end;
7.  
8. var
9.   myrec100: specialize tgenrec<dword, 100>; // project1.lpr(7,43) Error: Error in type definition
10.   myrec500: specialize tgenrec<dword, 500>; // project1.lpr(8,43) Error: Error in type definition
11.  
12. begin
13. end.

In older versions you can only really use the workaround you presented.

[Fibonacci]

This is great news, although I will need to upgrade this particular project to use newer version of FPC. Thanks though, didnt know it supported that in the trunk.