1 files changed, 44 insertions, 0 deletions
diff --git a/mfbt/Opaque.h b/mfbt/Opaque.h
new file mode 100644
index 0000000000..d7239ee7c2
--- /dev/null
+++ b/mfbt/Opaque.h
@@ -0,0 +1,44 @@
+/* -*- 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 */