1 // (C) Copyright 2008 CodeRage, LLC (turkanis at coderage dot com) 2 // (C) Copyright 2003-2007 Jonathan Turkanis 3 // Distributed under the Boost Software License, Version 1.0. (See accompanying 4 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt.) 5 6 // See http://www.boost.org/libs/iostreams for documentation. 7 8 // Contains the metafunction select, which mimics the effect of a chain of 9 // nested mpl if_'s. 10 // 11 // ----------------------------------------------------------------------------- 12 // 13 // Usage: 14 // 15 // typedef typename select< 16 // case1, type1, 17 // case2, type2, 18 // ... 19 // true_, typen 20 // >::type selection; 21 // 22 // Here case1, case2, ... are models of MPL::IntegralConstant with value type 23 // bool, and n <= 12. 24 25 #ifndef BOOST_IOSTREAMS_SELECT_HPP_INCLUDED 26 #define BOOST_IOSTREAMS_SELECT_HPP_INCLUDED 27 28 #if defined(_MSC_VER) 29 # pragma once 30 #endif 31 32 #include <boost/type_traits/is_base_and_derived.hpp> 33 #include <boost/mpl/eval_if.hpp> 34 #include <boost/mpl/identity.hpp> 35 #include <boost/mpl/if.hpp> 36 #include <boost/mpl/void.hpp> 37 38 namespace boost { namespace iostreams { 39 40 typedef mpl::true_ else_; 41 42 template< typename Case1 = mpl::true_, 43 typename Type1 = mpl::void_, 44 typename Case2 = mpl::true_, 45 typename Type2 = mpl::void_, 46 typename Case3 = mpl::true_, 47 typename Type3 = mpl::void_, 48 typename Case4 = mpl::true_, 49 typename Type4 = mpl::void_, 50 typename Case5 = mpl::true_, 51 typename Type5 = mpl::void_, 52 typename Case6 = mpl::true_, 53 typename Type6 = mpl::void_, 54 typename Case7 = mpl::true_, 55 typename Type7 = mpl::void_, 56 typename Case8 = mpl::true_, 57 typename Type8 = mpl::void_, 58 typename Case9 = mpl::true_, 59 typename Type9 = mpl::void_, 60 typename Case10 = mpl::true_, 61 typename Type10 = mpl::void_, 62 typename Case11 = mpl::true_, 63 typename Type11 = mpl::void_, 64 typename Case12 = mpl::true_, 65 typename Type12 = mpl::void_ > 66 struct select { 67 typedef typename 68 mpl::eval_if< 69 Case1, mpl::identity<Type1>, mpl::eval_if< 70 Case2, mpl::identity<Type2>, mpl::eval_if< 71 Case3, mpl::identity<Type3>, mpl::eval_if< 72 Case4, mpl::identity<Type4>, mpl::eval_if< 73 Case5, mpl::identity<Type5>, mpl::eval_if< 74 Case6, mpl::identity<Type6>, mpl::eval_if< 75 Case7, mpl::identity<Type7>, mpl::eval_if< 76 Case8, mpl::identity<Type8>, mpl::eval_if< 77 Case9, mpl::identity<Type9>, mpl::eval_if< 78 Case10, mpl::identity<Type10>, mpl::eval_if< 79 Case11, mpl::identity<Type11>, mpl::if_< 80 Case12, Type12, mpl::void_ > > > > > > > > > > > 81 >::type type; 82 }; 83 84 } } // End namespaces iostreams, boost. 85 86 #endif // #ifndef BOOST_IOSTREAMS_SELECT_HPP_INCLUDED 87