dom/indexedDB/FlippedOnce.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 file,
   5  * You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 #ifndef mozilla_dom_indexeddb_flippedonce_h__
   8 #define mozilla_dom_indexeddb_flippedonce_h__
   9
  10 #include "mozilla/Assertions.h"
  11 #include "mozilla/Attributes.h"
  12
  13 namespace mozilla {
  14
  15 // A state-restricted bool, which can only be flipped once. It isn't required to
  16 // be flipped during its lifetime.
  17 template <bool Initial>
  18 class FlippedOnce {
  19  public:
  20   FlippedOnce(const FlippedOnce&) = delete;
  21   FlippedOnce& operator=(const FlippedOnce&) = delete;
  22   FlippedOnce(FlippedOnce&&) = default;
  23   FlippedOnce& operator=(FlippedOnce&&) = default;
  24
  25   constexpr FlippedOnce() = default;
  26
  27   MOZ_IMPLICIT constexpr operator bool() const { return mValue; };
  28
  29   constexpr void Flip() {
  30     MOZ_ASSERT(mValue == Initial);
  31     EnsureFlipped();
  32   }
  33
  34   constexpr void EnsureFlipped() { mValue = !Initial; }
  35
  36  private:
  37   bool mValue = Initial;
  38 };
  39 }  // namespace mozilla
  40
  41 #endif