mfbt/EnumeratedArray.h

   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
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 /* EnumeratedArray is like Array, but indexed by a typed enum. */
   8
   9 #ifndef mozilla_EnumeratedArray_h
  10 #define mozilla_EnumeratedArray_h
  11
  12 #include "mozilla/Array.h"
  13
  14 namespace mozilla {
  15
  16 /**
  17  * EnumeratedArray is a fixed-size array container for use when an
  18  * array is indexed by a specific enum class.
  19  *
  20  * This provides type safety by guarding at compile time against accidentally
  21  * indexing such arrays with unrelated values. This also removes the need
  22  * for manual casting when using a typed enum value to index arrays.
  23  *
  24  * Aside from the typing of indices, EnumeratedArray is similar to Array.
  25  *
  26  * Example:
  27  *
  28  *   enum class AnimalSpecies {
  29  *     Cow,
  30  *     Sheep,
  31  *     Count
  32  *   };
  33  *
  34  *   EnumeratedArray<AnimalSpecies, AnimalSpecies::Count, int> headCount;
  35  *
  36  *   headCount[AnimalSpecies::Cow] = 17;
  37  *   headCount[AnimalSpecies::Sheep] = 30;
  38  *
  39  */
  40 template<typename IndexType,
  41          IndexType SizeAsEnumValue,
  42          typename ValueType>
  43 class EnumeratedArray
  44 {
  45 public:
  46   static const size_t kSize = size_t(SizeAsEnumValue);
  47
  48 private:
  49   Array<ValueType, kSize> mArray;
  50
  51 public:
  52   EnumeratedArray() {}
  53
  54   explicit EnumeratedArray(const EnumeratedArray& aOther)
  55   {
  56     for (size_t i = 0; i < kSize; i++) {
  57       mArray[i] = aOther.mArray[i];
  58     }
  59   }
  60
  61   ValueType& operator[](IndexType aIndex)
  62   {
  63     return mArray[size_t(aIndex)];
  64   }
  65
  66   const ValueType& operator[](IndexType aIndex) const
  67   {
  68     return mArray[size_t(aIndex)];
  69   }
  70 };
  71
  72 } // namespace mozilla
  73
  74 #endif // mozilla_EnumeratedArray_h