4.3. Exercises

4-0.	Write tests for mpl::or_ and mpl::and_ metafunctions that use their short-circuit behavior.
4-1.	Implement binary metafunctions called logical_or and logical_and that model the behavior of mpl::or_ and mpl::and_, correspondingly. Use tests from exercise 4-0 to verify your implementation.
4-2.	Extend the implementation of logical_or and logical_and metafunctions from exercise 4-1 to accept up to five arguments.
4-3.	Eliminate the unnecessary instantiations in the following code snippets: 1. template< typename N, typename Predicate > struct next_if : mpl::if_< typename mpl::apply<Predicate,N>::type , typename mpl::next<N>::type , N > {}; 2. template< typename N1, typename N2 > struct formula : mpl::if_< mpl::not_equal_to<N1,N2> , typename mpl::if_< mpl::greater<N1,N2> , typename mpl::minus<N1,N2>::type , N1 >::type , typename mpl::plus< N1 , typename mpl::multiplies<N1, mpl::int_<2> >::type >::type >::type {}; Write the tests to verify that the semantics of the transformed metafunctions remained unchanged.
4-4.	Use integral operators and the type traits library facilities to implement the following composite traits: is_data_member_pointer is_pointer_to_function is_reference_to_function_pointer is_reference_to_non_const
4-5.	Consider the following function template, which is designed to provide a "container-based" (as opposed to iterator-based) interface to std::find: template <class Container, class Value> typename Container::iterator container_find(Container& c, Value const& v) { return std::find(c.begin(), c.end(), v); } As coded, container_find won't work for const containers; Container will be deduced as const X for some container type X, but when we try to convert the Container::const_iterator returned by std::find into a Container::iterator, compilation will fail. Fix the problem using a small metaprogram to compute container_find's return type.