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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/* An opaque integral type supporting only comparison operators. */
+
+#ifndef mozilla_Opaque_h
+#define mozilla_Opaque_h
+
+#include "mozilla/TypeTraits.h"
+
+namespace mozilla {
+
+/**
+ * Opaque<T> is a replacement for integral T in cases where only comparisons
+ * must be supported, and it's desirable to prevent accidental dependency on
+ * exact values.
+ */
+template<typename T>
+class Opaque final
+{
+ static_assert(mozilla::IsIntegral<T>::value,
+ "mozilla::Opaque only supports integral types");
+
+ T mValue;
+
+public:
+ Opaque() {}
+ explicit Opaque(T aValue) : mValue(aValue) {}
+
+ bool operator==(const Opaque& aOther) const {
+ return mValue == aOther.mValue;
+ }
+
+ bool operator!=(const Opaque& aOther) const {
+ return !(*this == aOther);
+ }
+};
+
+} // namespace mozilla
+
+#endif /* mozilla_Opaque_h */