boost::mpl::for_each without instantiating

Question

Taking the following example, I wonder whether there is an alternative to boost::mpl::for_each, which does call a Functor without any arguments.

Answer 1

Use boost::type and mpl::_ to create an MPL lambda that transforms each type in the list before instantiating the elements and calling the function, like this:

mpl::for_each<Engines, boost::type<mpl::_> >(Registrator());

Registrator should look something like this:

struct Registrator
{
  template<typename T>
  void operator()(boost::type<T>) const
  {
      RegisterInFactory<EasyFixEngine, T> dummy(T::name());
  }
};

Hope that helps.

Answer 2

You should use the three parameter for_each:

mpl::for_each<Engines,mpl::single_view>(Registrator())

Then the instances you get will be of single_view.