mfbt/Opaque.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 /* An opaque integral type supporting only comparison operators. */
   8
   9 #ifndef mozilla_Opaque_h
  10 #define mozilla_Opaque_h
  11
  12 #include <type_traits>
  13
  14 namespace mozilla {
  15
  16 /**
  17  * Opaque<T> is a replacement for integral T in cases where only comparisons
  18  * must be supported, and it's desirable to prevent accidental dependency on
  19  * exact values.
  20  */
  21 template <typename T>
  22 class Opaque final {
  23   static_assert(std::is_integral_v<T>,
  24                 "mozilla::Opaque only supports integral types");
  25
  26   T mValue;
  27
  28  public:
  29   Opaque() = default;
  30   explicit Opaque(T aValue) : mValue(aValue) {}
  31
  32   bool operator==(const Opaque& aOther) const {
  33     return mValue == aOther.mValue;
  34   }
  35
  36   bool operator!=(const Opaque& aOther) const { return !(*this == aOther); }
  37 };
  38
  39 }  // namespace mozilla
  40
  41 #endif /* mozilla_Opaque_h */