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 #include "mozilla/TypedEnum.h"
  14
  15 namespace mozilla {
  16
  17 /**
  18  * EnumeratedArray is a fixed-size array container for use when an
  19  * array is indexed by a specific enum class, as currently implemented
  20  * by MOZ_BEGIN_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  *   MOZ_BEGIN_ENUM_CLASS(AnimalSpecies)
  31  *     Cow,
  32  *     Sheep,
  33  *     Count
  34  *   MOZ_END_ENUM_CLASS(AnimalSpecies)
  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,
  43          MOZ_TEMPLATE_ENUM_CLASS_ENUM_TYPE(IndexType) SizeAsEnumValue,
  44          typename ValueType>
  45 class EnumeratedArray
  46 {
  47 public:
  48   static const size_t kSize = size_t(SizeAsEnumValue);
  49
  50 private:
  51   Array<ValueType, kSize> mArray;
  52
  53 public:
  54   EnumeratedArray() {}
  55
  56   explicit EnumeratedArray(const EnumeratedArray& aOther)
  57   {
  58     for (size_t i = 0; i < kSize; i++) {
  59       mArray[i] = aOther.mArray[i];
  60     }
  61   }
  62
  63   ValueType& operator[](IndexType aIndex)
  64   {
  65     return mArray[size_t(aIndex)];
  66   }
  67
  68   const ValueType& operator[](IndexType aIndex) const
  69   {
  70     return mArray[size_t(aIndex)];
  71   }
  72 };
  73
  74 } // namespace mozilla
  75
  76 #endif // mozilla_EnumeratedArray_h