[fpc-pascal] Generic routines for both dynamic array and other collections

[Виктор Матузенко via fpc-pascal]

Hi,

I am trying to write some generic routines for working with containers. For
example, GetLength function:



unit u;

{$MODE FPC}
{$MODESWITCH DEFAULTPARAMETERS}
{$MODESWITCH OUT}
{$MODESWITCH RESULT}

interface

generic function GetLength<TContainter>(const V: TContainter): SizeUInt;

implementation

generic function GetLength<TContainter>(const V: TContainter): SizeUInt;
begin
  Exit(V.Count);
end;

end.


// the program
{$MODE FPC}
{$MODESWITCH DEFAULTPARAMETERS}
{$MODESWITCH OUT}
{$MODESWITCH RESULT}
{$MODESWITCH TYPEHELPERS}

uses
  u;

type
  TDynArray = array of PtrInt;

TDynArrayHelper = type helper for TDynArray
  function Count: SizeUInt;
end;

function TDynArrayHelper.Count: SizeUInt;
begin
  Exit(System.Length(Self));
end;

var
  V: TDynArray;

begin
  v := [0,  1,  2,  3,  5,  6,  7, 10, 11, 12,  13,  15,  16];
  Writeln(specialize GetLength<TDynArray>(v));
end.



It gives the following compilation error:
u.pas(16,10) Error: Illegal qualifier

Is the problem because the helper is not known while compiling the unit?

How do I write a generic routine GetLength which will work both for dynamic
arrays and for records, objects, classes with Count property?

-- 
Victor Matuzenko (Виктор Матузенко)

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