named_value.hh

/* vim: set sw=4 sts=4 et foldmethod=syntax : */
 
/*
 * Copyright (c) 2008, 2009, 2010 Ciaran McCreesh
 *
 * This file is part of the Paludis package manager. Paludis is free software;
 * you can redistribute it and/or modify it under the terms of the GNU General
 * Public License version 2, as published by the Free Software Foundation.
 *
 * Paludis is distributed in the hope that it will be useful, but WITHOUT ANY
 * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
 * FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more
 * details.
 *
 * You should have received a copy of the GNU General Public License along with
 * this program; if not, write to the Free Software Foundation, Inc., 59 Temple
 * Place, Suite 330, Boston, MA  02111-1307  USA
 */
 
#ifndef PALUDIS_GUARD_PALUDIS_UTIL_NAMED_VALUE_HH
#define PALUDIS_GUARD_PALUDIS_UTIL_NAMED_VALUE_HH 1
 
#include <paludis/util/named_value-fwd.hh>
#include <paludis/util/tribool.hh>
#include <utility>
#include <type_traits>
#include <string>
 
namespace paludis
{
    /**
     * A NamedValue is used to hold a member of type V_ for a class.
     *
     * NamedValue is used to simplify 'plain old data' style classes, and to
     * provide compiler-time-checked named parameters for functions. Use
     * thestruct.themember() and thestruct.themember() = to access the real
     * underlying values.
     *
     * Usually a struct containing NamedValue objects will be constructed using
     * the make_named_values() function. For each NamedValue object,
     * make_named_values() takes a parameter in the form
     * <code>n::whatever_K_is() = the_value</code>.
     *
     * In all cases, NamedValue members are listed in name-sorted order, and
     * the same name is used for K_ and the member name.
     *
     * \ingroup g_oo
     */
    template <typename K_, typename V_>
    class NamedValue
    {
        static_assert(! std::is_reference<V_>::value, "Tried to make a NamedValue hold a reference");
 
        private:
            V_ _value;
 
        public:
            typedef K_ KeyType;
            typedef V_ ValueType;
 
            template <typename T_>
            NamedValue(const NamedValue<K_, T_> & v) :
                _value(v())
            {
            }
 
            template <typename T_>
            NamedValue(NamedValue<K_, T_> && v) :
                _value(std::move(v()))
            {
            }
 
            explicit NamedValue(const V_ & v) :
                _value(v)
            {
            }
 
            explicit NamedValue(V_ && v) :
                _value(v)
            {
            }
 
            NamedValue(const NamedValue & v) = default;
 
            NamedValue(NamedValue && v) :
                _value(std::move(v._value))
            {
            }
 
            NamedValue & operator=(const NamedValue & v) = default;
 
            V_ & operator() ()
            {
                return _value;
            }
 
            const V_ & operator() () const
            {
                return _value;
            }
    };
 
    /**
     * A Name is used to make the assignment for NamedValue keys work.
     *
     * \ingroup g_oo
     */
    template <typename T_>
    class Name
    {
        public:
            template <typename V_>
            NamedValue<Name<T_>, V_> operator= (const V_ & v) const
            {
                return NamedValue<Name<T_>, V_>(v);
            }
 
            template <typename V_>
            NamedValue<Name<T_>, typename std::remove_reference<V_>::type> operator= (V_ && v) const
            {
                return NamedValue<Name<T_>, typename std::remove_reference<V_>::type>(v);
            }
 
            NamedValue<Name<T_>, std::string> operator= (const char * const v) const
            {
                return NamedValue<Name<T_>, std::string>(std::string(v));
            }
 
            NamedValue<Name<T_>, Tribool> operator= (TriboolIndeterminateValueType) const
            {
                return NamedValue<Name<T_>, Tribool>(Tribool(indeterminate));
            }
    };
}
 
#endif