Boost C++ Libraries

boost/spirit/home/x3/support/unused.hpp

/*=============================================================================
    Copyright (c) 2001-2014 Joel de Guzman
    Copyright (c) 2001-2011 Hartmut Kaiser

    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)
==============================================================================*/
#if !defined(BOOST_SPIRIT_X3_UNUSED_APRIL_16_2006_0616PM)
#define BOOST_SPIRIT_X3_UNUSED_APRIL_16_2006_0616PM

#include <iosfwd>

///////////////////////////////////////////////////////////////////////////////
namespace boost { namespace spirit { namespace x3
{
    struct unused_type
    {
        unused_type() = default;

        template <typename T>
        unused_type(T const&)
        {
        }

        template <typename T>
        unused_type const&
        operator=(T const&) const
        {
            return *this;
        }

        template <typename T>
        unused_type&
        operator=(T const&)
        {
            return *this;
        }

        // unused_type can also masquerade as an empty context (see context.hpp)

        template <typename ID>
        unused_type get(ID) const
        {
            return {};
        }

        friend std::ostream& operator<<(std::ostream& out, unused_type const&)
        {
            return out;
        }

        friend std::istream& operator>>(std::istream& in, unused_type&)
        {
            return in;
        }
    };

    constexpr auto unused = unused_type{};
}}}

#endif