uses System.Generics.Collections;

type
  TVehicle = class
  public
    procedure Test;
  end;

  TCar = class(TVehicle)
  end;

  TTruck = class(TVehicle)
  end;

procedure TVehicle.Test;
begin
  //ClassName reports the real type
  WriteLn('test ', ClassName);
end;

var
  List: TList<TVehicle>;
  Vehicle: TVehicle;
begin
  //descendants substitute for the base
  List := TList<TVehicle>.Create;
  List.Add(TVehicle.Create);
  List.Add(TCar.Create);
  List.Add(TTruck.Create);

  for Vehicle in List do
    Vehicle.Test;
end.