Generics.Defaults.TComparison Type

TComparison defines a generic callback function used to compare two generic values.

Pascal

TComparison<T> = reference to function(const Left, Right: T): Integer;

C++

reference to function(const Left, Right: T): Integer TComparison;

File

Generics.Defaults

Description

TComparison represents any routine capable of comparing two values of the same type. For example, CompareStr can be represented as TComparison<AnsiString>.

TComparison is primarily used together with the TDelegatedComparer class.

Delphi Examples:

Copy Code

{
This example demonstrates the usage of TDelegatedComparer and
anonymous methods in order to create a custom comparer.
The example assumes two memos and a button are present on the form.
}
procedure TForm3.Button1Click(Sender: TObject);
var
  List: TList<String>;
  Comparer: IComparer<String>;
  I: Integer;
begin
  { Create a new delegated comparer. We will use anonymous methods }
  Comparer := TDelegatedComparer<String>.Create(
    { TComparison<String> }
    function(const Left, Right: String): Integer
    begin
      { Consider the strings as numbers and return }
      { a comparison between them }
      Result := StrToInt(Left) - StrToInt(Right);
    end);

  { Create a new list of strings }
  List := TList<String>.Create(Comparer);

  { Populate the list with numbers in the memo }
  for I := 0 to InMemo.Lines.Count - 1 do
    List.Add(InMemo.Lines[I]);

  { Sort the list }
  List.Sort();

  { Copy the list with numbers to the memo }
  OutMemo.Clear;

  for I := 0 to List.Count - 1 do
    OutMemo.Lines.Add(List[I]);

  { Free resources }
  List.Free();
end;