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45 lines
1.8 KiB
C++
45 lines
1.8 KiB
C++
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// declval.hpp -------------------------------------------------------------//
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// Copyright 2010 Vicente J. Botet Escriba
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// Distributed under the Boost Software License, Version 1.0.
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// See http://www.boost.org/LICENSE_1_0.txt
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#ifndef BOOST_UTILITY_DECLVAL_HPP
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#define BOOST_UTILITY_DECLVAL_HPP
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#include <boost/config.hpp>
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//----------------------------------------------------------------------------//
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#include <boost/type_traits/add_rvalue_reference.hpp>
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//----------------------------------------------------------------------------//
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// //
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// C++03 implementation of //
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// 20.2.4 Function template declval [declval] //
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// Written by Vicente J. Botet Escriba //
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// //
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// 1 The library provides the function template declval to simplify the
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// definition of expressions which occur as unevaluated operands.
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// 2 Remarks: If this function is used, the program is ill-formed.
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// 3 Remarks: The template parameter T of declval may be an incomplete type.
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// [ Example:
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//
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// template <class To, class From>
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// decltype(static_cast<To>(declval<From>())) convert(From&&);
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//
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// declares a function template convert which only participates in overloading
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// if the type From can be explicitly converted to type To. For another example
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// see class template common_type (20.9.7.6). -end example ]
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//----------------------------------------------------------------------------//
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namespace boost {
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template <typename T>
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typename add_rvalue_reference<T>::type declval() BOOST_NOEXCEPT; // as unevaluated operand
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} // namespace boost
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#endif // BOOST_UTILITY_DECLVAL_HPP
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