ceph/src/boost/libs/ratio/example/type_traits/declval.hpp

   1 //  common_type.hpp  ---------------------------------------------------------//
   2
   3 //  Copyright 2010 Vicente J. Botet Escriba
   4
   5 //  Distributed under the Boost Software License, Version 1.0.
   6 //  See http://www.boost.org/LICENSE_1_0.txt
   7
   8 #ifndef BOOST_EX_TYPE_TRAITS_EXT_DECLVAL__HPP
   9 #define BOOST_EX_TYPE_TRAITS_EXT_DECLVAL__HPP
  10
  11 #include <boost/config.hpp>
  12
  13 //----------------------------------------------------------------------------//
  14
  15 #include "add_rvalue_reference.hpp"
  16
  17 //----------------------------------------------------------------------------//
  18 //                                                                            //
  19 //                           C++03 implementation of                          //
  20 //                          Written by Vicente J. Botet Escriba               //
  21 //~ 20.3.4 Function template declval [declval]
  22 //~ 1 The library provides the function template declval to simplify the definition of expressions which occur as
  23 //~ unevaluated operands.
  24 //~ 2 Remarks: If this function is used, the program is ill-formed.
  25 //~ 3 Remarks: The template parameter T of declval may be an incomplete type.
  26 //~ [ Example:
  27
  28 //~ template <class To, class From>
  29 //~ decltype(static_cast<To>(declval<From>())) convert(From&&);
  30
  31 //~ declares a function template convert which only participats in overloading if the type From can be
  32 //~ explicitly converted to type To. For another example see class template common_type (20.7.6.6). -end
  33 //~ example ]
  34 //                                                                            //
  35 //----------------------------------------------------------------------------//
  36
  37 namespace boost_ex {
  38
  39     template <typename T>
  40     typename add_rvalue_reference<T>::type declval(); //noexcept; // as unevaluated operand
  41
  42 }  // namespace boost
  43
  44 #endif  // BOOST_EX_TYPE_TRAITS_EXT_DECLVAL__HPP