default_constructible_unary_fn.hpp

Go to the documentation of this file.

// Boost.Range library
//
//  Copyright Neil Groves 2014. Use, modification and
//  distribution is subject to 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)
//
// For more information, see http://www.boost.org/libs/range/
//
#ifndef BOOST_RANGE_DETAIL_DEFAULT_CONSTRUCTIBLE_UNARY_FN_HPP_INCLUDED
#define BOOST_RANGE_DETAIL_DEFAULT_CONSTRUCTIBLE_UNARY_FN_HPP_INCLUDED

#include <utility>

#include <boost/mpl/if.hpp>
#include <boost/optional/optional.hpp>
#include <boost/type_traits/has_trivial_constructor.hpp>

namespace boost {
  namespace range_detail {

    template <typename F, typename R>
    class default_constructible_unary_fn_wrapper {
     public:
      typedef R result_type;

      default_constructible_unary_fn_wrapper() {}
      default_constructible_unary_fn_wrapper(const F &source)
          : m_impl(source) {}
      default_constructible_unary_fn_wrapper(
          const default_constructible_unary_fn_wrapper &source)
          : m_impl(source.m_impl) {}
      default_constructible_unary_fn_wrapper &operator=(
          const default_constructible_unary_fn_wrapper &source) {
        if (source.m_impl) {
          // Lambda are not copy/move assignable.
          m_impl.emplace(*source.m_impl);
        } else {
          m_impl.reset();
        }
        return *this;
      }
      template <typename Arg>
      R operator()(Arg &&arg) const {
        BOOST_ASSERT(m_impl);
        return (*m_impl)(std::forward<Arg>(arg));
      }

     private:
      boost::optional<F> m_impl;
    };

    template <typename F, typename R>
    struct default_constructible_unary_fn_gen {
      typedef typename boost::mpl::if_<
          boost::has_trivial_default_constructor<F>,
          F,
          default_constructible_unary_fn_wrapper<F, R> >::type type;
    };

  }  // namespace range_detail
}  // namespace boost

#endif  // include guard