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&) {}
    };

    struct set_extractor
    {
        template <class ValueType>
        struct apply
        {
            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
        };
    };

    struct map_extractor
    {
        template <class ValueType>
        struct apply
        {
            typedef ValueType value_type;
            typedef BOOST_DEDUCED_TYPENAME remove_const<BOOST_DEDUCED_TYPENAME ValueType::first_type>::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;
            }
/*
            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

        };
    };
}}

#endif