Common Patterns

Sometimes you need to get an instance of a certain Subject that has a globally unique combination of Traits. This can be thought of something like a singleton pattern within a classical OOP approach.

You can totally achieve that with the help of a simple method like this:<code cpp> template < typename T, typename …Ts > T GetSingleton(AMechanism* const Mechanism) {

  const auto Filter = FFilter::Make<T, Ts...>();
  const auto Chain = Mechanism->Enchain(Filter);

  auto Cursor = Chain->Iterate(0, 1);
  if (!Cursor.Provide())
  {
      checkNoEntry()
      return T();
  }
  const auto Trait = Cursor.GetTrait<T>();
  verifyf(!Cursor.Provide(), TEXT("Two singleton objects detected!"));
  return Trait;

} </cpp>