text: //          Copyright Carl Philipp Reh 2009 - 2021.
  // 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 FCPPT_EITHER_JOIN_HPP_INCLUDED
  #define FCPPT_EITHER_JOIN_HPP_INCLUDED
  
  #include <fcppt/move_if_rvalue.hpp>
  #include <fcppt/either/bind.hpp>
  #include <fcppt/either/failure_type.hpp>
  #include <fcppt/either/is_object_v.hpp>
  #include <fcppt/either/object_concept.hpp>
  #include <fcppt/either/object_impl.hpp>
  #include <fcppt/either/success_type.hpp>
  #include <fcppt/config/external_begin.hpp>
  #include <type_traits>
  #include <utility>
  #include <fcppt/config/external_end.hpp>
  
  namespace fcppt::either
  {
  /**
  \brief Removes one layer of eithers.
  
  \ingroup fcppteither
  
  If the outer either has failure <code>f_1</code>, then <code>f_1</code> is returned.
  Otherwise, if the inner either has failure <code>f_2</code>, then <code>f_2</code> is returned.
  Otherwise, the success value of the inner either is returned.
  */
  template <fcppt::either::object_concept Either>
  fcppt::either::object<
      fcppt::either::failure_type<Either>,
      fcppt::either::success_type<fcppt::either::success_type<Either>>>
  join(Either &&_either) requires fcppt::either::is_object_v<fcppt::either::success_type<Either>> &&
      std::is_same_v<
          fcppt::either::failure_type<Either>,
          fcppt::either::failure_type<fcppt::either::success_type<Either>>>
  {
    return fcppt::either::bind(
        std::forward<Either>(_either),
        [](auto &&_value) { return fcppt::move_if_rvalue<Either>(_value); });
  }
  }
  
  #endif
  