ceph/src/boost/boost/hof/identity.hpp

   1 /*=============================================================================
   2     Copyright (c) 2012 Paul Fultz II
   3     identity.h
   4     Distributed under the Boost Software License, Version 1.0. (See accompanying
   5     file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
   6 ==============================================================================*/
   7
   8 #ifndef BOOST_HOF_GUARD_FUNCTION_IDENTITY_H
   9 #define BOOST_HOF_GUARD_FUNCTION_IDENTITY_H
  10
  11 /// identity
  12 /// ========
  13 ///
  14 /// Description
  15 /// -----------
  16 ///
  17 /// The `identity` function is an unary function object that returns whats given to it.
  18 ///
  19 /// Semantics
  20 /// ---------
  21 ///
  22 ///     assert(identity(x) == x);
  23 ///
  24 /// Synopsis
  25 /// --------
  26 ///
  27 ///     template<class T>
  28 ///     constexpr T identity(T&& x);
  29 ///
  30
  31 #include <utility>
  32 #include <initializer_list>
  33 #include <boost/hof/detail/forward.hpp>
  34 #include <boost/hof/detail/static_const_var.hpp>
  35
  36 namespace boost { namespace hof { namespace identity_detail {
  37
  38 struct identity_base
  39 {
  40     template<class T>
  41     constexpr T operator()(T&& x) const
  42     noexcept(std::is_reference<T>::value || BOOST_HOF_IS_NOTHROW_MOVE_CONSTRUCTIBLE(T))
  43     {
  44         return BOOST_HOF_FORWARD(T)(x);
  45     }
  46
  47     template<class T>
  48     constexpr std::initializer_list<T>& operator()(std::initializer_list<T>& x) const noexcept
  49     {
  50         return x;
  51     }
  52
  53     template<class T>
  54     constexpr const std::initializer_list<T>& operator()(const std::initializer_list<T>& x) const noexcept
  55     {
  56         return x;
  57     }
  58
  59     template<class T>
  60     constexpr std::initializer_list<T> operator()(std::initializer_list<T>&& x) const noexcept(noexcept(std::initializer_list<T>(std::move(x))))
  61     {
  62         return BOOST_HOF_FORWARD(std::initializer_list<T>)(x);
  63     }
  64 };
  65
  66 }
  67
  68 BOOST_HOF_DECLARE_STATIC_VAR(identity, identity_detail::identity_base);
  69
  70 }} // namespace boost::hof
  71
  72 #endif