// *** before: ***
// a typed list was written by hand around TObjectList: a cast on every
// read, and nothing stopped you from adding the wrong object
type
  TPersonList = class(TObjectList)
  private
    function GetItem(Index: Integer): TPerson;
  public
    property Items[Index: Integer]: TPerson read GetItem; default;
  end;

function TPersonList.GetItem(Index: Integer): TPerson;
begin
  Result := TPerson(inherited Items[Index]);
end;

// *** in version 2009: ***
uses
  Generics.Collections;

type
  // your own generic type: one declaration serves every element type
  TBox<T> = record
    Value: T;
    function IsEmpty: Boolean;
  end;

var
  People: TList<TPerson>;
  Ages: TDictionary<string, Integer>;
begin
  People := TList<TPerson>.Create;
  People.Add(TPerson.Create('Anna'));
  Writeln(People[0].Name);      // no cast - the compiler knows the type
  // People.Add(42) does not compile any more

  Ages := TDictionary<string, Integer>.Create;
  Ages.Add('Anna', 31);
  Writeln(Ages['Anna']);
end;