Chris@16: // (C) Copyright David Abrahams 2002.
Chris@16: // (C) Copyright Jeremy Siek    2002.
Chris@16: // (C) Copyright Thomas Witt    2002.
Chris@16: // Distributed under the Boost Software License, Version 1.0. (See
Chris@16: // accompanying file LICENSE_1_0.txt or copy at
Chris@16: // http://www.boost.org/LICENSE_1_0.txt)
Chris@16: #ifndef BOOST_ENABLE_IF_23022003THW_HPP
Chris@16: #define BOOST_ENABLE_IF_23022003THW_HPP
Chris@16: 
Chris@16: #include <boost/detail/workaround.hpp>
Chris@16: #include <boost/mpl/identity.hpp>
Chris@16: 
Chris@16: #include <boost/iterator/detail/config_def.hpp>
Chris@16: 
Chris@16: //
Chris@16: // Boost iterators uses its own enable_if cause we need
Chris@16: // special semantics for deficient compilers.
Chris@16: // 23/02/03 thw
Chris@16: //
Chris@16: 
Chris@16: namespace boost
Chris@16: {
Chris@16: 
Chris@16:   namespace iterators
Chris@16:   {
Chris@16:     //
Chris@16:     // Base machinery for all kinds of enable if
Chris@16:     //
Chris@16:     template<bool>
Chris@16:     struct enabled
Chris@16:     {
Chris@16:       template<typename T>
Chris@16:       struct base
Chris@16:       {
Chris@16:         typedef T type;
Chris@16:       };
Chris@16:     };
Chris@101: 
Chris@16:     //
Chris@16:     // For compilers that don't support "Substitution Failure Is Not An Error"
Chris@16:     // enable_if falls back to always enabled. See comments
Chris@16:     // on operator implementation for consequences.
Chris@16:     //
Chris@16:     template<>
Chris@16:     struct enabled<false>
Chris@16:     {
Chris@16:       template<typename T>
Chris@16:       struct base
Chris@16:       {
Chris@16: #ifdef BOOST_NO_SFINAE
Chris@16: 
Chris@16:         typedef T type;
Chris@16: 
Chris@16:         // This way to do it would give a nice error message containing
Chris@16:         // invalid overload, but has the big disadvantage that
Chris@16:         // there is no reference to user code in the error message.
Chris@16:         //
Chris@16:         // struct invalid_overload;
Chris@16:         // typedef invalid_overload type;
Chris@16:         //
Chris@16: #endif
Chris@16:       };
Chris@16:     };
Chris@16: 
Chris@16: 
Chris@16:     template <class Cond,
Chris@16:               class Return>
Chris@16:     struct enable_if
Chris@16: # if !defined(BOOST_NO_SFINAE) && !defined(BOOST_NO_IS_CONVERTIBLE)
Chris@16:       : enabled<(Cond::value)>::template base<Return>
Chris@16: # else
Chris@16:       : mpl::identity<Return>
Chris@101: # endif
Chris@16:     {
Chris@16:     };
Chris@16: 
Chris@16:   } // namespace iterators
Chris@16: 
Chris@16: } // namespace boost
Chris@16: 
Chris@16: #include <boost/iterator/detail/config_undef.hpp>
Chris@16: 
Chris@16: #endif // BOOST_ENABLE_IF_23022003THW_HPP