從 TListT 下降使其具體化
type
  TIntegerList = class(TList<Integer>)
  public
    function Sum: Integer;
  end;
...
function TIntegerList.Sum: Integer;
var
  Item: Integer;
begin
  Result := 0;
  for Item in Self do
     Result := Result + Item;
end;
type
  TIntegerList = class(TList<Integer>)
  public
    function Sum: Integer;
  end;
...
function TIntegerList.Sum: Integer;
var
  Item: Integer;
begin
  Result := 0;
  for Item in Self do
     Result := Result + Item;
end;