| 1 | // declval.hpp -------------------------------------------------------------// |
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| 2 | |
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| 3 | // Copyright 2010 Vicente J. Botet Escriba |
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| 4 | |
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| 5 | // Distributed under the Boost Software License, Version 1.0. |
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| 6 | // See http://www.boost.org/LICENSE_1_0.txt |
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| 7 | |
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| 8 | #ifndef BOOST_TYPE_TRAITS_DECLVAL_HPP_INCLUDED |
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| 9 | #define BOOST_TYPE_TRAITS_DECLVAL_HPP_INCLUDED |
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| 10 | |
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| 11 | #include <boost/config.hpp> |
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| 12 | |
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| 13 | //----------------------------------------------------------------------------// |
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| 14 | |
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| 15 | #include <boost/type_traits/add_rvalue_reference.hpp> |
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| 16 | |
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| 17 | //----------------------------------------------------------------------------// |
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| 18 | // // |
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| 19 | // C++03 implementation of // |
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| 20 | // 20.2.4 Function template declval [declval] // |
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| 21 | // Written by Vicente J. Botet Escriba // |
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| 22 | // // |
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| 23 | // 1 The library provides the function template declval to simplify the |
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| 24 | // definition of expressions which occur as unevaluated operands. |
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| 25 | // 2 Remarks: If this function is used, the program is ill-formed. |
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| 26 | // 3 Remarks: The template parameter T of declval may be an incomplete type. |
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| 27 | // [ Example: |
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| 28 | // |
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| 29 | // template <class To, class From> |
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| 30 | // decltype(static_cast<To>(declval<From>())) convert(From&&); |
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| 31 | // |
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| 32 | // declares a function template convert which only participates in overloading |
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| 33 | // if the type From can be explicitly converted to type To. For another example |
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| 34 | // see class template common_type (20.9.7.6). -end example ] |
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| 35 | //----------------------------------------------------------------------------// |
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| 36 | |
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| 37 | namespace boost { |
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| 38 | |
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| 39 | template <typename T> |
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| 40 | typename add_rvalue_reference<T>::type declval() BOOST_NOEXCEPT; // as unevaluated operand |
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| 41 | |
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| 42 | } // namespace boost |
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| 43 | |
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| 44 | #endif // BOOST_TYPE_TRAITS_DECLVAL_HPP_INCLUDED |
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| 45 | |
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