Added boost header

test/external/boost/utility/declval.hpp

@@ -0,0 +1,44 @@
+//  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>
+
+//----------------------------------------------------------------------------//
+//                                                                            //
+//                           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). <20>end
+//~ example ]
+//                                                                            //
+//----------------------------------------------------------------------------//
+
+namespace boost {
+
+    template <typename T>
+    typename add_rvalue_reference<T>::type declval(); //noexcept; // as unevaluated operand
+
+}  // namespace boost
+
+#endif  // BOOST_TYPE_TRAITS_EXT_DECLVAL__HPP