Struct template is_impl_ptr<T, void_type< typename T::impl_ptr

Struct template is_impl_ptr<T, void_type< typename T::impl_ptr_type >>

boost::is_impl_ptr<T, void_type< typename T::impl_ptr_type >>

// In header: <impl_ptr.hpp>

template<typename T> 
struct is_impl_ptr<T, void_type< typename T::impl_ptr_type >> : public true_type {
};