Enums.h

//
// Copyright (c) 2014-present, Facebook, Inc.
// All rights reserved.
//
// This source code is licensed under the University of Illinois/NCSA Open
// Source License found in the LICENSE file in the root directory of this
// source tree. An additional grant of patent rights can be found in the
// PATENTS file in the same directory.
//
 
#pragma once
 
#include <type_traits>
 
template <typename Enum> struct EnableBitMaskOperators {
  static const bool enable = false;
};
 
template <typename Enum>
typename std::enable_if<EnableBitMaskOperators<Enum>::enable,
                        Enum>::type constexpr
operator|(Enum lhs, Enum rhs) {
  using Underlying = typename std::underlying_type<Enum>::type;
  return static_cast<Enum>(static_cast<Underlying>(lhs) |
                           static_cast<Underlying>(rhs));
}
 
template <typename Enum>
typename std::enable_if<EnableBitMaskOperators<Enum>::enable,
                        Enum>::type constexpr
operator&(Enum lhs, Enum rhs) {
  using Underlying = typename std::underlying_type<Enum>::type;
  return static_cast<Enum>(static_cast<Underlying>(lhs) &
                           static_cast<Underlying>(rhs));
}
 
template <typename Enum>
typename std::enable_if<EnableBitMaskOperators<Enum>::enable,
                        Enum>::type constexpr
operator~(Enum e) {
  using Underlying = typename std::underlying_type<Enum>::type;
  return static_cast<Enum>(~static_cast<Underlying>(e));
}
 
template <typename Enum>
typename std::enable_if<EnableBitMaskOperators<Enum>::enable,
                        Enum>::type constexpr
operator!(Enum e) {
  using Underlying = typename std::underlying_type<Enum>::type;
  return static_cast<Enum>(!static_cast<Underlying>(e));
}
 
#define ENABLE_BITMASK_OPERATORS(x)                                            \
  template <> struct EnableBitMaskOperators<x> {                               \
    static const bool enable = true;                                           \
  }