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+
+// Copyright (C) 2005-2011 Daniel James
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#ifndef BOOST_UNORDERED_DETAIL_EXTRACT_KEY_HPP_INCLUDED
+#define BOOST_UNORDERED_DETAIL_EXTRACT_KEY_HPP_INCLUDED
+
+#include <boost/config.hpp>
+#if defined(BOOST_HAS_PRAGMA_ONCE)
+#pragma once
+#endif
+
+#include <boost/unordered/detail/table.hpp>
+
+namespace boost {
+namespace unordered {
+namespace detail {
+
+    // key extractors
+    //
+    // no throw
+    //
+    // 'extract_key' is called with the emplace parameters to return a
+    // key if available or 'no_key' is one isn't and will need to be
+    // constructed. This could be done by overloading the emplace implementation
+    // for the different cases, but that's a bit tricky on compilers without
+    // variadic templates.
+
+    struct no_key {
+        no_key() {}
+        template <class T> no_key(T const&) {}
+    };
+
+    template <typename Key, typename T>
+    struct is_key {
+        template <typename T2>
+        static choice1::type test(T2 const&);
+        static choice2::type test(Key const&);
+        
+        enum { value = sizeof(test(boost::unordered::detail::make<T>())) ==
+            sizeof(choice2::type) };
+        
+        typedef typename boost::detail::if_true<value>::
+            BOOST_NESTED_TEMPLATE then<Key const&, no_key>::type type;
+    };
+
+    template <class ValueType>
+    struct set_extractor
+    {
+        typedef ValueType value_type;
+        typedef ValueType key_type;
+
+        static key_type const& extract(value_type const& v)
+        {
+            return v;
+        }
+
+        static no_key extract()
+        {
+            return no_key();
+        }
+        
+        template <class Arg>
+        static no_key extract(Arg const&)
+        {
+            return no_key();
+        }
+
+#if !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES)
+        template <class Arg1, class Arg2, class... Args>
+        static no_key extract(Arg1 const&, Arg2 const&, Args const&...)
+        {
+            return no_key();
+        }
+#else
+        template <class Arg1, class Arg2>
+        static no_key extract(Arg1 const&, Arg2 const&)
+        {
+            return no_key();
+        }
+#endif
+    };
+
+    template <class Key, class ValueType>
+    struct map_extractor
+    {
+        typedef ValueType value_type;
+        typedef typename boost::remove_const<Key>::type key_type;
+
+        static key_type const& extract(value_type const& v)
+        {
+            return v.first;
+        }
+            
+        template <class Second>
+        static key_type const& extract(std::pair<key_type, Second> const& v)
+        {
+            return v.first;
+        }
+
+        template <class Second>
+        static key_type const& extract(
+            std::pair<key_type const, Second> const& v)
+        {
+            return v.first;
+        }
+
+        template <class Arg1>
+        static key_type const& extract(key_type const& k, Arg1 const&)
+        {
+            return k;
+        }
+
+        static no_key extract()
+        {
+            return no_key();
+        }
+
+        template <class Arg>
+        static no_key extract(Arg const&)
+        {
+            return no_key();
+        }
+
+        template <class Arg1, class Arg2>
+        static no_key extract(Arg1 const&, Arg2 const&)
+        {
+            return no_key();
+        }
+
+#if !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES)
+        template <class Arg1, class Arg2, class Arg3, class... Args>
+        static no_key extract(Arg1 const&, Arg2 const&, Arg3 const&,
+                Args const&...)
+        {
+            return no_key();
+        }
+#endif
+
+#if !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES)
+
+#define BOOST_UNORDERED_KEY_FROM_TUPLE(namespace_)                          \
+        template <typename T2>                                              \
+        static no_key extract(boost::unordered::piecewise_construct_t,      \
+                namespace_ tuple<> const&, T2 const&)                       \
+        {                                                                   \
+            return no_key();                                                \
+        }                                                                   \
+                                                                            \
+        template <typename T, typename T2>                                  \
+        static typename is_key<key_type, T>::type                           \
+            extract(boost::unordered::piecewise_construct_t,                \
+                namespace_ tuple<T> const& k, T2 const&)                    \
+        {                                                                   \
+            return typename is_key<key_type, T>::type(                      \
+                namespace_ get<0>(k));                                      \
+        }
+
+#else
+
+#define BOOST_UNORDERED_KEY_FROM_TUPLE(namespace_)                          \
+        static no_key extract(boost::unordered::piecewise_construct_t,      \
+                namespace_ tuple<> const&)                                  \
+        {                                                                   \
+            return no_key();                                                \
+        }                                                                   \
+                                                                            \
+        template <typename T>                                               \
+        static typename is_key<key_type, T>::type                           \
+            extract(boost::unordered::piecewise_construct_t,                \
+                namespace_ tuple<T> const& k)                               \
+        {                                                                   \
+            return typename is_key<key_type, T>::type(                      \
+                namespace_ get<0>(k));                                      \
+        }
+
+#endif
+
+BOOST_UNORDERED_KEY_FROM_TUPLE(boost::)
+
+#if !defined(BOOST_NO_CXX11_HDR_TUPLE)
+BOOST_UNORDERED_KEY_FROM_TUPLE(std::)
+#endif
+    };
+}}}
+
+#endif