boost/iostreams/detail/select.hpp
// (C) Copyright 2008 CodeRage, LLC (turkanis at coderage dot com) // (C) Copyright 2003-2007 Jonathan Turkanis // 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.) // See http://www.boost.org/libs/iostreams for documentation. // Contains the metafunction select, which mimics the effect of a chain of // nested mpl if_'s. // // ----------------------------------------------------------------------------- // // Usage: // // typedef typename select< // case1, type1, // case2, type2, // ... // true_, typen // >::type selection; // // Here case1, case2, ... are models of MPL::IntegralConstant with value type // bool, and n <= 12. #ifndef BOOST_IOSTREAMS_SELECT_HPP_INCLUDED #define BOOST_IOSTREAMS_SELECT_HPP_INCLUDED #if defined(_MSC_VER) && (_MSC_VER >= 1020) # pragma once #endif #include <boost/type_traits/is_base_and_derived.hpp> #include <boost/mpl/eval_if.hpp> #include <boost/mpl/identity.hpp> #include <boost/mpl/if.hpp> #include <boost/mpl/void.hpp> namespace boost { namespace iostreams { typedef mpl::true_ else_; template< typename Case1 = mpl::true_, typename Type1 = mpl::void_, typename Case2 = mpl::true_, typename Type2 = mpl::void_, typename Case3 = mpl::true_, typename Type3 = mpl::void_, typename Case4 = mpl::true_, typename Type4 = mpl::void_, typename Case5 = mpl::true_, typename Type5 = mpl::void_, typename Case6 = mpl::true_, typename Type6 = mpl::void_, typename Case7 = mpl::true_, typename Type7 = mpl::void_, typename Case8 = mpl::true_, typename Type8 = mpl::void_, typename Case9 = mpl::true_, typename Type9 = mpl::void_, typename Case10 = mpl::true_, typename Type10 = mpl::void_, typename Case11 = mpl::true_, typename Type11 = mpl::void_, typename Case12 = mpl::true_, typename Type12 = mpl::void_ > struct select { typedef typename mpl::eval_if< Case1, mpl::identity<Type1>, mpl::eval_if< Case2, mpl::identity<Type2>, mpl::eval_if< Case3, mpl::identity<Type3>, mpl::eval_if< Case4, mpl::identity<Type4>, mpl::eval_if< Case5, mpl::identity<Type5>, mpl::eval_if< Case6, mpl::identity<Type6>, mpl::eval_if< Case7, mpl::identity<Type7>, mpl::eval_if< Case8, mpl::identity<Type8>, mpl::eval_if< Case9, mpl::identity<Type9>, mpl::eval_if< Case10, mpl::identity<Type10>, mpl::eval_if< Case11, mpl::identity<Type11>, mpl::if_< Case12, Type12, mpl::void_ > > > > > > > > > > > >::type type; }; } } // End namespaces iostreams, boost. #endif // #ifndef BOOST_IOSTREAMS_SELECT_HPP_INCLUDED