exec_if.h

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#pragma once
// Copyright Aleksey Gurtovoy 2000-2008
//
// 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)
//
// See http://www.boost.org/libs/mpl for documentation.

// $Id: exec_if.hpp 55648 2009-08-18 05:16:53Z agurtovoy $
// $Date: 2009-08-17 22:16:53 -0700 (Mon, 17 Aug 2009) $
// $Revision: 55648 $

#include <boost/mpl/apply.hpp>
#include <boost/mpl/assert.hpp>
#include <boost/mpl/aux_/unwrap.hpp>
#include <boost/mpl/begin_end.hpp>
#include <boost/mpl/bool.hpp>
#include <boost/mpl/deref.hpp>
#include <boost/mpl/identity.hpp>
#include <boost/mpl/is_sequence.hpp>
#include <boost/mpl/next_prior.hpp>

#include <boost/type_traits/is_same.hpp>
#include <boost/utility/value_init.hpp>

namespace boost {
namespace mpl {

namespace aux {

template <bool done = true> struct exec_if_impl {
  template <typename Iterator, typename LastIterator, typename TransformFunc,
            typename F>
  static bool execute(Iterator *, LastIterator *, TransformFunc *, F) {
    return true;
  }
};

template <> struct exec_if_impl<false> {
  template <typename Iterator, typename LastIterator, typename TransformFunc,
            typename F>
  static bool execute(Iterator *, LastIterator *, TransformFunc *, F f) {
    typedef typename deref<Iterator>::type item;
    typedef typename apply1<TransformFunc, item>::type arg;

    // dwa 2002/9/10 -- make sure not to invoke undefined behavior
    // when we pass arg.
    value_initialized<arg> x;
    // Only execute further actions if return from the current action is true
    if (aux::unwrap(f, 0)(boost::get(x))) {
      typedef typename mpl::next<Iterator>::type iter;
      return exec_if_impl<boost::is_same<iter, LastIterator>::value>::execute(
          static_cast<iter *>(0), static_cast<LastIterator *>(0),
          static_cast<TransformFunc *>(0), f);
    }
    return false;
  }
};

} // namespace aux

// agurt, 17/mar/02: pointer default parameters are necessary to workaround
// MSVC 6.5 function template signature's mangling bug
template <typename Sequence, typename TransformOp, typename F>
inline bool exec_if(F f, Sequence * = 0, TransformOp * = 0) {
  BOOST_MPL_ASSERT((is_sequence<Sequence>));

  typedef typename begin<Sequence>::type first;
  typedef typename end<Sequence>::type last;

  return aux::exec_if_impl<boost::is_same<first, last>::value>::execute(
      static_cast<first *>(0), static_cast<last *>(0),
      static_cast<TransformOp *>(0), f);
}

template <typename Sequence, typename F>
inline bool exec_if(F f, Sequence * = 0) {
  return exec_if<Sequence, identity<>>(f);
}
}
}