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
37namespace 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