boost/utility/declval.hpp
// common_type.hpp ---------------------------------------------------------// // Copyright 2010 Vicente J. Botet Escriba // Distributed under the Boost Software License, Version 1.0. // See http://www.boost.org/LICENSE_1_0.txt #ifndef BOOST_TYPE_TRAITS_EXT_DECLVAL__HPP #define BOOST_TYPE_TRAITS_EXT_DECLVAL__HPP #include <boost/config.hpp> //----------------------------------------------------------------------------// #include <boost/type_traits/add_rvalue_reference.hpp> //#include <boost/type_traits/add_lvalue_reference.hpp> //----------------------------------------------------------------------------// // // // C++03 implementation of // // Written by Vicente J. Botet Escriba // //~ 20.3.4 Function template declval [declval] //~ 1 The library provides the function template declval to simplify the definition of expressions which occur as //~ unevaluated operands. //~ 2 Remarks: If this function is used, the program is ill-formed. //~ 3 Remarks: The template parameter T of declval may be an incomplete type. //~ [ Example: //~ template <class To, class From> //~ decltype(static_cast<To>(declval<From>())) convert(From&&); //~ declares a function template convert which only participats in overloading if the type From can be //~ explicitly converted to type To. For another example see class template common_type (20.7.6.6). �end //~ example ] // // //----------------------------------------------------------------------------// namespace boost { //#if !defined(BOOST_NO_RVALUE_REFERENCES) template <typename T> typename add_rvalue_reference<T>::type declval() BOOST_NOEXCEPT; // as unevaluated operand //#else // template <typename T> // typename add_lvalue_reference<T>::type declval() BOOST_NOEXCEPT; // as unevaluated operand //#endif } // namespace boost #endif // BOOST_TYPE_TRAITS_EXT_DECLVAL__HPP