williamr@2: //-----------------------------------------------------------------------------
williamr@2: // boost variant/visitor_ptr.hpp header file
williamr@2: // See http://www.boost.org for updates, documentation, and revision history.
williamr@2: //-----------------------------------------------------------------------------
williamr@2: //
williamr@2: // Copyright (c) 2002-2003
williamr@2: // Eric Friedman
williamr@2: //
williamr@2: // Distributed under the Boost Software License, Version 1.0. (See
williamr@2: // accompanying file LICENSE_1_0.txt or copy at
williamr@2: // http://www.boost.org/LICENSE_1_0.txt)
williamr@2: 
williamr@2: #ifndef BOOST_VARIANT_VISITOR_PTR_HPP
williamr@2: #define BOOST_VARIANT_VISITOR_PTR_HPP
williamr@2: 
williamr@2: #include "boost/variant/bad_visit.hpp"
williamr@2: #include "boost/variant/static_visitor.hpp"
williamr@2: 
williamr@2: #include "boost/mpl/eval_if.hpp"
williamr@2: #include "boost/mpl/identity.hpp"
williamr@2: #include "boost/type_traits/add_reference.hpp"
williamr@2: #include "boost/type_traits/is_reference.hpp"
williamr@2: #include "boost/type_traits/is_void.hpp"
williamr@2: 
williamr@2: namespace boost {
williamr@2: 
williamr@2: //////////////////////////////////////////////////////////////////////////
williamr@2: // function template visitor_ptr
williamr@2: //
williamr@2: // Adapts a function pointer for use as visitor capable of handling
williamr@2: // values of a single type. Throws bad_visit if inappropriately applied.
williamr@2: //
williamr@2: template <typename T, typename R>
williamr@2: class visitor_ptr_t
williamr@2:     : public static_visitor<R>
williamr@2: {
williamr@2: private: // representation
williamr@2: 
williamr@2:     typedef R (*visitor_t)(T);
williamr@2: 
williamr@2:     visitor_t visitor_;
williamr@2: 
williamr@2: public: // typedefs
williamr@2: 
williamr@2:     typedef R result_type;
williamr@2: 
williamr@2: private: // private typedefs
williamr@2: 
williamr@2:     typedef typename mpl::eval_if<
williamr@2:           is_reference<T>
williamr@2:         , mpl::identity<T>
williamr@2:         , add_reference<const T>
williamr@2:         >::type argument_fwd_type;
williamr@2: 
williamr@2: public: // structors
williamr@2: 
williamr@2:     explicit visitor_ptr_t(visitor_t visitor)
williamr@2:       : visitor_(visitor)
williamr@2:     {
williamr@2:     }
williamr@2: 
williamr@2: public: // static visitor interfaces
williamr@2: 
williamr@2:     template <typename U>
williamr@2:     result_type operator()(const U&) const
williamr@2:     {
williamr@2:         throw bad_visit();
williamr@2:     }
williamr@2: 
williamr@2: #if !defined(BOOST_NO_VOID_RETURNS)
williamr@2: 
williamr@2: public: // static visitor interfaces, cont.
williamr@2: 
williamr@2:     result_type operator()(argument_fwd_type operand) const
williamr@2:     {
williamr@2:         return visitor_(operand);
williamr@2:     }
williamr@2: 
williamr@2: #else // defined(BOOST_NO_VOID_RETURNS)
williamr@2: 
williamr@2: private: // helpers, for static visitor interfaces (below)
williamr@2: 
williamr@2:     result_type execute_impl(argument_fwd_type operand, mpl::false_) const
williamr@2:     {
williamr@2:         return visitor_(operand);
williamr@2:     }
williamr@2: 
williamr@2:         BOOST_VARIANT_AUX_RETURN_VOID_TYPE
williamr@2:     execute_impl(argument_fwd_type operand, mpl::true_) const
williamr@2:     {
williamr@2:         visitor_(operand);
williamr@2:         BOOST_VARIANT_AUX_RETURN_VOID;
williamr@2:     }
williamr@2: 
williamr@2: public: // static visitor interfaces, cont.
williamr@2: 
williamr@2:         BOOST_VARIANT_AUX_GENERIC_RESULT_TYPE(result_type)
williamr@2:     operator()(argument_fwd_type operand) const
williamr@2:     {
williamr@2:         typedef typename is_void<result_type>::type has_void_result;
williamr@2:         return execute_impl(operand, has_void_result());
williamr@2:     }
williamr@2: 
williamr@2: #endif // BOOST_NO_VOID_RETURNS workaround
williamr@2: 
williamr@2: };
williamr@2: 
williamr@2: template <typename R, typename T>
williamr@2: inline visitor_ptr_t<T,R> visitor_ptr(R (*visitor)(T))
williamr@2: {
williamr@2:     return visitor_ptr_t<T,R>(visitor);
williamr@2: }
williamr@2: 
williamr@2: } // namespace boost
williamr@2: 
williamr@2: #endif// BOOST_VISITOR_VISITOR_PTR_HPP