1 // declval.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_TYPE_TRAITS_DECLVAL_HPP_INCLUDED 9 #define BOOST_TYPE_TRAITS_DECLVAL_HPP_INCLUDED 10 11 #include <boost/config.hpp> 12 13 //----------------------------------------------------------------------------// 14 15 #include <boost/type_traits/add_rvalue_reference.hpp> 16 17 //----------------------------------------------------------------------------// 18 // // 19 // C++03 implementation of // 20 // 20.2.4 Function template declval [declval] // 21 // Written by Vicente J. Botet Escriba // 22 // // 23 // 1 The library provides the function template declval to simplify the 24 // definition of expressions which occur as unevaluated operands. 25 // 2 Remarks: If this function is used, the program is ill-formed. 26 // 3 Remarks: The template parameter T of declval may be an incomplete type. 27 // [ Example: 28 // 29 // template <class To, class From> 30 // decltype(static_cast<To>(declval<From>())) convert(From&&); 31 // 32 // declares a function template convert which only participates in overloading 33 // if the type From can be explicitly converted to type To. For another example 34 // see class template common_type (20.9.7.6). -end example ] 35 //----------------------------------------------------------------------------// 36 37 namespace boost { 38 39 template <typename T> 40 typename add_rvalue_reference<T>::type declval() BOOST_NOEXCEPT; // as unevaluated operand 41 42 } // namespace boost 43 44 #endif // BOOST_TYPE_TRAITS_DECLVAL_HPP_INCLUDED 45