Re: IInterfaceList and Sort

From: John Elrick (jelrick_at_adelphia.net)
Date: 10/28/03 

Date: Tue, 28 Oct 2003 08:59:32 -0500

"Harley Pebley" <harley_pebley@idahotech.com> wrote in message
news:1n5r48nl1akd7$.3owk6fzxcgb.dlg@40tude.net...
> > I generate a collection of Interfaces and add them to a
> > IInterfaceList. Unfortunately there is no Sort method.
> >
> > What is the easiest way to sort such a collection?
>
> Create one:
> ISortedInterfaceList = interface(IInterfaceList)
> procedure Sort;
> end;

A more generic approach:

TCompareResult= (crLessThan, crEqual, crGreaterThan);

{ descend from this interface for specific uses
   Example:
   IIntegerComparable = interface(IComparable)
     function asInteger: integer;
   end;

  TIntegerComparable = class(TInterfacedObject, IIntegerComparable,
IComparable)
     function compare(const aComparator: IComparable): TCompareResult;
     function asInteger: integer;
  end;

function TIntegerComparable.compare(const aComparator: IComparable):
TCompareResult;
var
  localCompare: integer;
begin
  localCompare := (aComparator as IIntegerComparable).asInteger;
  if asInteger = localCompare then
    result := crEqual
  else if asInteger < localCompare then
    result := crLessThan
  else
    result := crGreaterThan;
end;

 }
IComparable = interface
  function compare(const aComparator: IComparable): TCompareResult;
end;

ISortable = interface
  function get_Item(const aIndex: integer): IComparable;
  function Count: integer;
  procedure Exchange(const aFirstIndex, aSecondIndex: integer);
end;

ISorter = interface
  procedure Sort(const aSortable: ISortable);
end;

TQuickSort = class(TInterfacedObject, ISorter)
  procedure Sort(const aSortable: ISortable);
end;

TTreeSort = class(TInterfacedObject, ISorter)
  procedure Sort(const aSortable: ISortable);
end;

{ Hey, why not<g> }
TBubbleSort = class(TInterfacedObject, ISorter)
  procedure Sort(const aSortable: ISortable);
end;

ISortedInterfaceList = interface

  procedure Sort;
 end;

> TSortedInterfaceList = class(TInterfaceList, IInterfaceList, ISortable,
ISortedList)
> procedure Sort;

  function get_Item(const aIndex: integer): IComparable;
  procedure Exchange(const aFirstIndex, aSecondIndex: integer);
> end;
>

procedure TSortedInterfaceList.Sort;
var
  localSorter : ISorter;
begin
  localSorter := TQuickSort.Create;
  localSorter.Sort(Self);
end;

TQuickSort.Sort can be modified from TList. The nice part is that once it's
written to take IComparable and ISortable, the sort routine will work with
_any_ implementor.

FWIW

John

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