1 // declval.hpp -------------------------------------------------------------//
3 // Copyright 2010 Vicente J. Botet Escriba
5 // Distributed under the Boost Software License, Version 1.0.
6 // See http://www.boost.org/LICENSE_1_0.txt
8 #ifndef BOOST_TYPE_TRAITS_DECLVAL_HPP_INCLUDED
9 #define BOOST_TYPE_TRAITS_DECLVAL_HPP_INCLUDED
11 #include <boost/config.hpp>
13 //----------------------------------------------------------------------------//
15 #include <boost/type_traits/add_rvalue_reference.hpp>
17 //----------------------------------------------------------------------------//
19 // C++03 implementation of //
20 // 20.2.4 Function template declval [declval] //
21 // Written by Vicente J. Botet Escriba //
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.
29 // template <class To, class From>
30 // decltype(static_cast<To>(declval<From>())) convert(From&&);
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 //----------------------------------------------------------------------------//
40 typename add_rvalue_reference<T>::type declval() BOOST_NOEXCEPT; // as unevaluated operand
44 #endif // BOOST_TYPE_TRAITS_DECLVAL_HPP_INCLUDED