ceph/src/boost/boost/mp11/detail/mp_front.hpp

   1 #ifndef BOOST_MP11_DETAIL_MP_FRONT_HPP_INCLUDED
   2 #define BOOST_MP11_DETAIL_MP_FRONT_HPP_INCLUDED
   3
   4 //  Copyright 2015-2021 Peter Dimov.
   5 //
   6 //  Distributed under the Boost Software License, Version 1.0.
   7 //
   8 //  See accompanying file LICENSE_1_0.txt or copy at
   9 //  http://www.boost.org/LICENSE_1_0.txt
  10
  11 namespace boost
  12 {
  13 namespace mp11
  14 {
  15
  16 // mp_front<L>
  17 namespace detail
  18 {
  19
  20 template<class L> struct mp_front_impl
  21 {
  22 // An error "no type named 'type'" here means that the argument to mp_front
  23 // is either not a list, or is an empty list
  24 };
  25
  26 template<template<class...> class L, class T1, class... T> struct mp_front_impl<L<T1, T...>>
  27 {
  28     using type = T1;
  29 };
  30
  31 } // namespace detail
  32
  33 template<class L> using mp_front = typename detail::mp_front_impl<L>::type;
  34
  35 } // namespace mp11
  36 } // namespace boost
  37
  38 #endif // #ifndef BOOST_MP11_DETAIL_MP_FRONT_HPP_INCLUDED