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