text: #ifndef OPAQUE_INCONVERTIBOOL_HPP
  #define OPAQUE_INCONVERTIBOOL_HPP
  //
  // Copyright (c) 2015, 2016, 2021
  // Kyle Markley.  All rights reserved.
  //
  // Redistribution and use in source and binary forms, with or without
  // modification, are permitted provided that the following conditions are met:
  //
  // 1. Redistributions of source code must retain the above copyright notice,
  //    this list of conditions and the following disclaimer.
  // 2. Redistributions in binary form must reproduce the above copyright notice,
  //    this list of conditions and the following disclaimer in the documentation
  //    and/or other materials provided with the distribution.
  // 3. Neither the name of the author nor the names of any contributors may be
  //    used to endorse or promote products derived from this software without
  //    specific prior written permission.
  //
  // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
  // AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  // IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  // ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
  // LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
  // CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
  // SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
  // INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
  // CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
  // ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  // POSSIBILITY OF SUCH DAMAGE.
  //
  #include "opaque/numeric_typedef.hpp"
  
  namespace opaque {
  
  /// \addtogroup typedefs
  /// @{
  
  ///
  /// Safer boolean type.  May be implicitly created from a bool, but not
  /// from any other type, and which is not implicitly convertible to any type.
  ///
  /// This is a safer substitute for built-in bool if you are concerned about
  /// implicit conversions of bool to and from other types (like int) that may
  /// be bugs.  Inconvertibool prevents those implicit conversions.
  ///
  /// By request of Christoph Weiss.
  ///
  struct inconvertibool : opaque::numeric_typedef<bool, inconvertibool> {
    using base = opaque::numeric_typedef<bool, inconvertibool>;
    inconvertibool() = default;
  
    // Constructor is not explicit, but is hidden for types other than bool.
    template <typename T, typename = typename std::enable_if<
      std::is_same<bool, typename std::decay<T>::type>::value>::type>
    constexpr inconvertibool(T initial) noexcept : base(initial) { }
  };
  
  constexpr inline bool operator==(bool b, const inconvertibool& i) noexcept {
    return b == i.value;
  }
  constexpr inline bool operator!=(bool b, const inconvertibool& i) noexcept {
    return b != i.value;
  }
  
  /// @}
  
  }
  
  #endif
  