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Filename : fail_to_compile_observers.hpp
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/* Policies for result and outcome
(C) 2018-2020 Niall Douglas <http://www.nedproductions.biz/> (4 commits)
File Created: Sep 2018


Boost Software License - Version 1.0 - August 17th, 2003

Permission is hereby granted, free of charge, to any person or organization
obtaining a copy of the software and accompanying documentation covered by
this license (the "Software") to use, reproduce, display, distribute,
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do so, all subject to the following:

The copyright notices in the Software and this entire statement, including
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must be included in all copies of the Software, in whole or in part, and
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SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE
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*/

#ifndef BOOST_OUTCOME_POLICY_FAIL_TO_COMPILE_OBSERVERS_HPP
#define BOOST_OUTCOME_POLICY_FAIL_TO_COMPILE_OBSERVERS_HPP

#include "base.hpp"

BOOST_OUTCOME_V2_NAMESPACE_EXPORT_BEGIN

#define BOOST_OUTCOME_FAIL_TO_COMPILE_OBSERVERS_MESSAGE                                                                                                                                                                                                                                                                              \
  "Attempt to wide observe value, error or "                                                                                                                                                                                                                                                                                   \
  "exception for a basic_result/basic_outcome given an EC or EP type which is not void, and for whom "                                                                                                                                                                                                                         \
  "trait::is_error_code_available<EC>, trait::is_exception_ptr_available<EC>, and trait::is_exception_ptr_available<EP> "                                                                                                                                                                                                      \
  "are all false. Please specify a NoValuePolicy to tell basic_result/basic_outcome what to do, or else use "                                                                                                                                                                                                                  \
  "a more specific convenience type alias such as unchecked<T, E> to indicate you want the wide "                                                                                                                                                                                                                              \
  "observers to be narrow, or checked<T, E> to indicate you always want an exception throw etc."

namespace policy
{
  struct fail_to_compile_observers : base
  {
    template <class Impl> static constexpr void wide_value_check(Impl && /* unused */) { static_assert(!std::is_same<Impl, Impl>::value, BOOST_OUTCOME_FAIL_TO_COMPILE_OBSERVERS_MESSAGE); }
    template <class Impl> static constexpr void wide_error_check(Impl && /* unused */) { static_assert(!std::is_same<Impl, Impl>::value, BOOST_OUTCOME_FAIL_TO_COMPILE_OBSERVERS_MESSAGE); }
    template <class Impl> static constexpr void wide_exception_check(Impl && /* unused */) { static_assert(!std::is_same<Impl, Impl>::value, BOOST_OUTCOME_FAIL_TO_COMPILE_OBSERVERS_MESSAGE); }
  };
}  // namespace policy

#undef BOOST_OUTCOME_FAIL_TO_COMPILE_OBSERVERS_MESSAGE

BOOST_OUTCOME_V2_NAMESPACE_END

#endif