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 <utility>
  13
  14 #include "mozilla/Array.h"
  15
  16 namespace mozilla {
  17
  18 /**
  19  * EnumeratedArray is a fixed-size array container for use when an
  20  * array is indexed by a specific enum class.
  21  *
  22  * This provides type safety by guarding at compile time against accidentally
  23  * indexing such arrays with unrelated values. This also removes the need
  24  * for manual casting when using a typed enum value to index arrays.
  25  *
  26  * Aside from the typing of indices, EnumeratedArray is similar to Array.
  27  *
  28  * Example:
  29  *
  30  *   enum class AnimalSpecies {
  31  *     Cow,
  32  *     Sheep,
  33  *     Count
  34  *   };
  35  *
  36  *   EnumeratedArray<AnimalSpecies, AnimalSpecies::Count, int> headCount;
  37  *
  38  *   headCount[AnimalSpecies::Cow] = 17;
  39  *   headCount[AnimalSpecies::Sheep] = 30;
  40  *
  41  */
  42 template <typename IndexType, IndexType SizeAsEnumValue, typename ValueType>
  43 class EnumeratedArray {
  44  public:
  45   static const size_t kSize = size_t(SizeAsEnumValue);
  46
  47  private:
  48   typedef Array<ValueType, kSize> ArrayType;
  49
  50   ArrayType mArray;
  51
  52  public:
  53   EnumeratedArray() = default;
  54
  55   template <typename... Args>
  56   MOZ_IMPLICIT constexpr EnumeratedArray(Args&&... aArgs)
  57       : mArray{std::forward<Args>(aArgs)...} {}
  58
  59   ValueType& operator[](IndexType aIndex) { return mArray[size_t(aIndex)]; }
  60
  61   const ValueType& operator[](IndexType aIndex) const {
  62     return mArray[size_t(aIndex)];
  63   }
  64
  65   typedef typename ArrayType::iterator iterator;
  66   typedef typename ArrayType::const_iterator const_iterator;
  67   typedef typename ArrayType::reverse_iterator reverse_iterator;
  68   typedef typename ArrayType::const_reverse_iterator const_reverse_iterator;
  69
  70   // Methods for range-based for loops.
  71   iterator begin() { return mArray.begin(); }
  72   const_iterator begin() const { return mArray.begin(); }
  73   const_iterator cbegin() const { return mArray.cbegin(); }
  74   iterator end() { return mArray.end(); }
  75   const_iterator end() const { return mArray.end(); }
  76   const_iterator cend() const { return mArray.cend(); }
  77
  78   // Methods for reverse iterating.
  79   reverse_iterator rbegin() { return mArray.rbegin(); }
  80   const_reverse_iterator rbegin() const { return mArray.rbegin(); }
  81   const_reverse_iterator crbegin() const { return mArray.crbegin(); }
  82   reverse_iterator rend() { return mArray.rend(); }
  83   const_reverse_iterator rend() const { return mArray.rend(); }
  84   const_reverse_iterator crend() const { return mArray.crend(); }
  85 };
  86
  87 }  // namespace mozilla
  88
  89 #endif  // mozilla_EnumeratedArray_h