boost_unordered/include/boost/unordered/detail/extract_key.hpp

// Copyright (C) 2005-2009 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>
#include <boost/type_traits/remove_const.hpp>
#include <boost/unordered/detail/fwd.hpp>

namespace boost {
namespace unordered_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 <class ValueType>
    struct set_extractor
    {
        typedef ValueType value_type;
        typedef ValueType key_type;

        static key_type const& extract(key_type const& v)
        {
            return v;
        }

        static no_key extract()
        {
            return no_key();
        }
        
#if defined(BOOST_UNORDERED_STD_FORWARD)
        template <class... Args>
        static no_key extract(Args const&...)
        {
            return no_key();
        }

#else
        template <class Arg>
        static no_key extract(Arg const&)
        {
            return no_key();
        }

        template <class Arg>
        static no_key extract(Arg const&, Arg const&)
        {
            return no_key();
        }
#endif

        static bool compare_mapped(value_type const&, value_type const&)
        {
            return true;
        }
    };

    template <class Key, class ValueType>
    struct map_extractor
    {
        typedef ValueType value_type;
        typedef BOOST_DEDUCED_TYPENAME boost::remove_const<Key>::type key_type;

        static key_type const& extract(value_type const& v)
        {
            return v.first;
        }
            
        static key_type const& extract(key_type const& v)
        {
            return v;
        }

        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;
        }

#if defined(BOOST_UNORDERED_STD_FORWARD)
        template <class Arg1, class... Args>
        static key_type const& extract(key_type const& k,
            Arg1 const&, Args const&...)
        {
            return k;
        }

        template <class... Args>
        static no_key extract(Args const&...)
        {
            return no_key();
        }
#else
        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 Arg, class Arg1>
        static no_key extract(Arg const&, Arg1 const&)
        {
            return no_key();
        }
#endif

        static bool compare_mapped(value_type const& x, value_type const& y)
        {
            return x.second == y.second;
        }
    };
}}

#endif