[Lazarus] *** SPAM *** How to pass function method to TList.Sort?

[Howard Page-Clark]

On 09/12/2015 20:11, Donald Ziesig wrote:
> Is there any way to pass a method function as the Compare parameter to 
> a TList or is there a work around for it?
> As in:
>
> type
>   TMyClass = object
>      fIndex : Integer;
>      List : array of TList;
>      function Compare( Item1, Item2 : Pointer) : Longint; // needs 
> access to fIndex
>
>      procedure Sort;
>   end;
>
> implementation
>
> function TMyClass.Compare( Item1, Item2 : Pointer ) : Longint;
> begin
>    case fIndex of
>       0:  Result := some compare of Item1, Item2;// These compares are 
> implemented in an object from another unit
>       1:  Result := another compare of Item1, Item2
>    end;
> end;
>
> procedure TMyClass.Sort;
> begin
>   fIndex := 0;
>   List[fIndex].Sort( @Compare );  // Compilation error, doesn't like 
> Compare being "of object"
> end;

It's a dreadful hack, but you could try something like:

type
   TClassListSortCompare = function (Item1, Item2: Pointer): Integer of 
object;

procedure TMyClass.Sort;
var
   objectFunction: TClassListSortCompare;
   regularFunction: TListSortCompare;
begin
   fIndex := 0;
   objectFunction:=@Compare;
   regularFunction:=TListSortCompare(TMethod(objectFunction).Code);
   List[fIndex].Sort( regularFunction );
end;


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