Boost C++ Libraries

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boost/mp11/detail/mp_front.hpp

#ifndef BOOST_MP11_DETAIL_MP_FRONT_HPP_INCLUDED
#define BOOST_MP11_DETAIL_MP_FRONT_HPP_INCLUDED

//  Copyright 2015-2021 Peter Dimov.
//
//  Distributed under the Boost Software License, Version 1.0.
//
//  See accompanying file LICENSE_1_0.txt or copy at
//  http://www.boost.org/LICENSE_1_0.txt

namespace boost
{
namespace mp11
{

// mp_front<L>
namespace detail
{

template<class L> struct mp_front_impl
{
// An error "no type named 'type'" here means that the argument to mp_front
// is either not a list, or is an empty list
};

template<template<class...> class L, class T1, class... T> struct mp_front_impl<L<T1, T...>>
{
    using type = T1;
};

} // namespace detail

template<class L> using mp_front = typename detail::mp_front_impl<L>::type;

} // namespace mp11
} // namespace boost

#endif // #ifndef BOOST_MP11_DETAIL_MP_FRONT_HPP_INCLUDED