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diff --git a/mfbt/EnumeratedArray.h b/mfbt/EnumeratedArray.h
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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/. */
+
+/* EnumeratedArray is like Array, but indexed by a typed enum. */
+
+#ifndef mozilla_EnumeratedArray_h
+#define mozilla_EnumeratedArray_h
+
+#include "mozilla/Array.h"
+#include "mozilla/Move.h"
+
+namespace mozilla {
+
+/**
+ * EnumeratedArray is a fixed-size array container for use when an
+ * array is indexed by a specific enum class.
+ *
+ * This provides type safety by guarding at compile time against accidentally
+ * indexing such arrays with unrelated values. This also removes the need
+ * for manual casting when using a typed enum value to index arrays.
+ *
+ * Aside from the typing of indices, EnumeratedArray is similar to Array.
+ *
+ * Example:
+ *
+ *   enum class AnimalSpecies {
+ *     Cow,
+ *     Sheep,
+ *     Count
+ *   };
+ *
+ *   EnumeratedArray<AnimalSpecies, AnimalSpecies::Count, int> headCount;
+ *
+ *   headCount[AnimalSpecies::Cow] = 17;
+ *   headCount[AnimalSpecies::Sheep] = 30;
+ *
+ */
+template<typename IndexType,
+         IndexType SizeAsEnumValue,
+         typename ValueType>
+class EnumeratedArray
+{
+public:
+  static const size_t kSize = size_t(SizeAsEnumValue);
+
+private:
+  typedef Array<ValueType, kSize> ArrayType;
+
+  ArrayType mArray;
+
+public:
+  EnumeratedArray() {}
+
+  template <typename... Args>
+  MOZ_IMPLICIT EnumeratedArray(Args&&... aArgs)
+    : mArray{mozilla::Forward<Args>(aArgs)...}
+  {}
+
+  explicit EnumeratedArray(const EnumeratedArray& aOther)
+  {
+    for (size_t i = 0; i < kSize; i++) {
+      mArray[i] = aOther.mArray[i];
+    }
+  }
+
+  EnumeratedArray(EnumeratedArray&& aOther)
+  {
+    for (size_t i = 0; i < kSize; i++) {
+      mArray[i] = Move(aOther.mArray[i]);
+    }
+  }
+
+  ValueType& operator[](IndexType aIndex)
+  {
+    return mArray[size_t(aIndex)];
+  }
+
+  const ValueType& operator[](IndexType aIndex) const
+  {
+    return mArray[size_t(aIndex)];
+  }
+
+  typedef typename ArrayType::iterator               iterator;
+  typedef typename ArrayType::const_iterator         const_iterator;
+  typedef typename ArrayType::reverse_iterator       reverse_iterator;
+  typedef typename ArrayType::const_reverse_iterator const_reverse_iterator;
+
+  // Methods for range-based for loops.
+  iterator begin() { return mArray.begin(); }
+  const_iterator begin() const { return mArray.begin(); }
+  const_iterator cbegin() const { return mArray.cbegin(); }
+  iterator end() { return mArray.end(); }
+  const_iterator end() const { return mArray.end(); }
+  const_iterator cend() const { return mArray.cend(); }
+
+  // Methods for reverse iterating.
+  reverse_iterator rbegin() { return mArray.rbegin(); }
+  const_reverse_iterator rbegin() const { return mArray.rbegin(); }
+  const_reverse_iterator crbegin() const { return mArray.crbegin(); }
+  reverse_iterator rend() { return mArray.rend(); }
+  const_reverse_iterator rend() const { return mArray.rend(); }
+  const_reverse_iterator crend() const { return mArray.crend(); }
+};
+
+} // namespace mozilla
+
+#endif // mozilla_EnumeratedArray_h