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// boost variant/visitor_ptr.hpp header file
// See for updates, documentation, and revision history.
// Copyright (c) 2002-2003
// Eric Friedman
// Distributed under the Boost Software License, Version 1.0. (See
// accompanying file LICENSE_1_0.txt or copy at


#include "boost/variant/bad_visit.hpp"
#include "boost/variant/static_visitor.hpp"

#include "boost/mpl/eval_if.hpp"
#include "boost/mpl/identity.hpp"
#include "boost/type_traits/add_reference.hpp"
#include "boost/type_traits/is_reference.hpp"
#include "boost/type_traits/is_void.hpp"

namespace boost {

// function template visitor_ptr
// Adapts a function pointer for use as visitor capable of handling
// values of a single type. Throws bad_visit if inappropriately applied.
template <typename T, typename R>
class visitor_ptr_t
    : public static_visitor<R>
private: // representation

    typedef R (*visitor_t)(T);

    visitor_t visitor_;

public: // typedefs

    typedef R result_type;

private: // private typedefs

    typedef typename mpl::eval_if<
        , mpl::identity<T>
        , add_reference<const T>
        >::type argument_fwd_type;

public: // structors

    explicit visitor_ptr_t(visitor_t visitor)
      : visitor_(visitor)

public: // static visitor interfaces

    template <typename U>
    result_type operator()(const U&) const
        throw bad_visit();


public: // static visitor interfaces, cont.

    result_type operator()(argument_fwd_type operand) const
        return visitor_(operand);

#else // defined(BOOST_NO_VOID_RETURNS)

private: // helpers, for static visitor interfaces (below)

    result_type execute_impl(argument_fwd_type operand, mpl::false_) const
        return visitor_(operand);

    execute_impl(argument_fwd_type operand, mpl::true_) const

public: // static visitor interfaces, cont.

    operator()(argument_fwd_type operand) const
        typedef typename is_void<result_type>::type has_void_result;
        return execute_impl(operand, has_void_result());

#endif // BOOST_NO_VOID_RETURNS workaround


template <typename R, typename T>
inline visitor_ptr_t<T,R> visitor_ptr(R (*visitor)(T))
    return visitor_ptr_t<T,R>(visitor);

} // namespace boost