apply.hpp

The following code example is taken from the book
C++ Templates - The Complete Guide, 2nd Edition
by David Vandevoorde, Nicolai M. Josuttis, and Douglas Gregor,
Addison-Wesley, 2017
© Copyright David Vandevoorde, Nicolai M. Josuttis, Douglas Gregor 2017


template<typename F, typename... Elements, unsigned... Indices>
auto applyImpl(F f, Tuple<Elements...> const& t,
                    Valuelist<unsigned, Indices...>)
  ->decltype(f(get<Indices>(t)...))
{
  return f(get<Indices>(t)...);
}

template<typename F, typename... Elements, 
         unsigned N = sizeof...(Elements)>
auto apply(F f, Tuple<Elements...> const& t) 
  ->decltype(applyImpl(f, t, MakeIndexList<N>()))
{
  return applyImpl(f, t, MakeIndexList<N>());
}