FlippedOnce.h (1186B)
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