Re: [fpc-devel]Nested function as argument for TList.Sort

[Marc Weustink]

At 08:54 27-11-2003, Florian Klaempfl wrote:
Pedro Lopez-Cabanillas wrote:

Hi,
The attached program compiles and works fine under Kylix 3, and also 
compiles under fpc 1.9, but bombs with this message:
An unhandled exception occurred at 0x0807F0B5 :
EAccessViolation : Access violation
  0x0807F0B5
It happens on TObjectList.Sort when the argument is a local nested 
function. It works well when the argument is a global function.
Regards,
Pedro

------------------------------------------------------------------------
program test6;
{$IFDEF FPC}
  {$MODE DELPHI}
{$ENDIF}
uses
  Contnrs;
type
  TestClass = class
  private
    key: Integer;
  public
    constructor Create(keyValue: Integer);
    function getKey: Integer;
  end;
  constructor TestClass.Create(keyValue: Integer);
  begin
    key := keyValue;
  end;
  function TestClass.getKey: Integer;
  begin
    Result := key;
  end;
var
  list: TObjectList;
  procedure Populate;
  begin
    list := TObjectList.Create;
    list.add(TestClass.Create(10));
    list.add(TestClass.Create(5));
    list.add(TestClass.Create(25));
    list.add(TestClass.Create(15));
  end;
  procedure SortAndPrint;
    function TestCompare(ptr1, ptr2: pointer): Integer;
    var
      int1, int2: Integer;
    begin
      int1 := TestClass(ptr1).getKey;
      int2 := TestClass(ptr2).getKey;
      if int1 = int2
      then Result := 0
      else if int1 < int2
           then Result := -1
           else Result := 1;
    end;
  var
    i: Integer;
  begin
    list.Sort(@TestCompare);
    for i := 0 to list.Count-1 do
    begin
      WriteLn('Item ', i, ', key = ', TestClass(list.Items[i]).getKey);
    end;
  end;
begin
  Populate;
  SortAndPrint;
end.
This is bad coding imho and works in Delphi only "by accident" because 
Delphi uses register calling conventions. Or are I'am wrong and sort 
expects a local procedure?
AFAIK it is illegal in D5 to use a local procedure for TList.Sort. Don't 
know if it is still the case in later versions (I haven't tried it and 
don't expect it)  In D1 (or earlier ?) it was legal to do this

Marc



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