//----------------------------------------------------------------------------- // boost variant/get.hpp header file // See http://www.boost.org for updates, documentation, and revision history. //----------------------------------------------------------------------------- // // Copyright (c) 2003 // Eric Friedman, Itay Maman // // 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_VARIANT_GET_HPP #define BOOST_VARIANT_GET_HPP #include <exception> #include "boost/config.hpp" #include "boost/detail/workaround.hpp" #include "boost/utility/addressof.hpp" #include "boost/variant/variant_fwd.hpp" #include "boost/type_traits/add_reference.hpp" #include "boost/type_traits/add_pointer.hpp" #if BOOST_WORKAROUND(BOOST_MSVC, < 1300) # include "boost/mpl/bool.hpp" # include "boost/mpl/or.hpp" # include "boost/type_traits/is_same.hpp" #endif namespace boost { ////////////////////////////////////////////////////////////////////////// // class bad_get // // The exception thrown in the event of a failed get of a value. // class bad_get : public std::exception { public: // std::exception implementation virtual const char * what() const throw() { return "boost::bad_get: " "failed value get using boost::get"; } }; ////////////////////////////////////////////////////////////////////////// // function template get<T> // // Retrieves content of given variant object if content is of type T. // Otherwise: pointer ver. returns 0; reference ver. throws bad_get. // namespace detail { namespace variant { // (detail) class template get_visitor // // Generic static visitor that: if the value is of the specified type, // returns a pointer to the value it visits; else a null pointer. // template <typename T> struct get_visitor { private: // private typedefs typedef typename add_pointer<T>::type pointer; typedef typename add_reference<T>::type reference; public: // visitor typedefs typedef pointer result_type; public: // visitor interfaces #if !BOOST_WORKAROUND(BOOST_MSVC, < 1300) pointer operator()(reference operand) const { return boost::addressof(operand); } template <typename U> pointer operator()(const U&) const { return static_cast<pointer>(0); } #else // MSVC6 private: // helpers, for visitor interfaces (below) pointer execute_impl(reference operand, mpl::true_) const { return boost::addressof(operand); } template <typename U> pointer execute_impl(const U& operand, mpl::false_) const { return static_cast<pointer>(0); } public: // visitor interfaces template <typename U> pointer operator()(U& operand) const { // MSVC6 finds normal implementation (above) ambiguous, // so we must explicitly disambiguate typedef typename mpl::or_< is_same<U, T> , is_same<const U, T> >::type U_is_T; return execute_impl(operand, U_is_T()); } #endif // MSVC6 workaround }; }} // namespace detail::variant #if !BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x0551)) # define BOOST_VARIANT_AUX_GET_EXPLICIT_TEMPLATE_TYPE(t) \ BOOST_APPEND_EXPLICIT_TEMPLATE_TYPE(t) #else # define BOOST_VARIANT_AUX_GET_EXPLICIT_TEMPLATE_TYPE(t) \ , t* = 0 #endif template <typename U, BOOST_VARIANT_ENUM_PARAMS(typename T) > inline typename add_pointer<U>::type get( boost::variant< BOOST_VARIANT_ENUM_PARAMS(T) >* operand BOOST_VARIANT_AUX_GET_EXPLICIT_TEMPLATE_TYPE(U) ) { typedef typename add_pointer<U>::type U_ptr; if (!operand) return static_cast<U_ptr>(0); detail::variant::get_visitor<U> v; return operand->apply_visitor(v); } template <typename U, BOOST_VARIANT_ENUM_PARAMS(typename T) > inline typename add_pointer<const U>::type get( const boost::variant< BOOST_VARIANT_ENUM_PARAMS(T) >* operand BOOST_VARIANT_AUX_GET_EXPLICIT_TEMPLATE_TYPE(U) ) { typedef typename add_pointer<const U>::type U_ptr; if (!operand) return static_cast<U_ptr>(0); detail::variant::get_visitor<const U> v; return operand->apply_visitor(v); } template <typename U, BOOST_VARIANT_ENUM_PARAMS(typename T) > inline typename add_reference<U>::type get( boost::variant< BOOST_VARIANT_ENUM_PARAMS(T) >& operand BOOST_VARIANT_AUX_GET_EXPLICIT_TEMPLATE_TYPE(U) ) { typedef typename add_pointer<U>::type U_ptr; U_ptr result = get<U>(&operand); if (!result) throw bad_get(); return *result; } template <typename U, BOOST_VARIANT_ENUM_PARAMS(typename T) > inline typename add_reference<const U>::type get( const boost::variant< BOOST_VARIANT_ENUM_PARAMS(T) >& operand BOOST_VARIANT_AUX_GET_EXPLICIT_TEMPLATE_TYPE(U) ) { typedef typename add_pointer<const U>::type U_ptr; U_ptr result = get<const U>(&operand); if (!result) throw bad_get(); return *result; } } // namespace boost #endif // BOOST_VARIANT_GET_HPP