1 files changed, 41 insertions, 0 deletions
diff --git a/mfbt/Opaque.h b/mfbt/Opaque.h
new file mode 100644
index 0000000000..e5dc84f159
--- /dev/null
+++ b/mfbt/Opaque.h
@@ -0,0 +1,41 @@
+/* -*- 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 <type_traits>
+
+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(std::is_integral_v<T>,
+                "mozilla::Opaque only supports integral types");
+
+  T mValue;
+
+ public:
+  Opaque() = default;
+  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 */