mfbt/Buffer.h

   1 /* This Source Code Form is subject to the terms of the Mozilla Public
   2  * License, v. 2.0. If a copy of the MPL was not distributed with this
   3  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   4
   5 #ifndef mozilla_Buffer_h
   6 #define mozilla_Buffer_h
   7
   8 #include <algorithm>
   9 #include "mozilla/Maybe.h"
  10 #include "mozilla/Span.h"
  11 #include "mozilla/UniquePtr.h"
  12 #include "mozilla/UniquePtrExtensions.h"
  13
  14 namespace mozilla {
  15
  16 /**
  17  * A move-only type that wraps a mozilla::UniquePtr<T[]> and the length of
  18  * the T[].
  19  *
  20  * Unlike mozilla::Array, the length is a run-time property.
  21  * Unlike mozilla::Vector and nsTArray, does not have capacity and
  22  * assocatiated growth functionality.
  23  * Unlike mozilla::Span, mozilla::Buffer owns the allocation it points to.
  24  */
  25 template <typename T>
  26 class Buffer final {
  27  private:
  28   mozilla::UniquePtr<T[]> mData;
  29   size_t mLength;
  30
  31  public:
  32   Buffer(const Buffer<T>& aOther) = delete;
  33   Buffer<T>& operator=(const Buffer<T>& aOther) = delete;
  34
  35   /**
  36    * Construct zero-lenth Buffer (without actually pointing to a heap
  37    * allocation).
  38    */
  39   Buffer() : mData(nullptr), mLength(0){};
  40
  41   /**
  42    * Construct from raw parts.
  43    *
  44    * aLength must not be greater than the actual length of the buffer pointed
  45    * to by aData.
  46    */
  47   Buffer(mozilla::UniquePtr<T[]>&& aData, size_t aLength)
  48       : mData(std::move(aData)), mLength(aLength) {}
  49
  50   /**
  51    * Move constructor. Sets the moved-from Buffer to zero-length
  52    * state.
  53    */
  54   Buffer(Buffer<T>&& aOther)
  55       : mData(std::move(aOther.mData)), mLength(aOther.mLength) {
  56     aOther.mLength = 0;
  57   }
  58
  59   /**
  60    * Construct by copying the elements of a Span.
  61    *
  62    * Allocates the internal buffer infallibly. Use CopyFrom for fallible
  63    * allocation.
  64    */
  65   explicit Buffer(mozilla::Span<const T> aSpan)
  66       : mData(mozilla::MakeUnique<T[]>(aSpan.Length())),
  67         mLength(aSpan.Length()) {
  68     std::copy(aSpan.cbegin(), aSpan.cend(), mData.get());
  69   }
  70
  71   /**
  72    * Create a new Buffer by copying the elements of a Span.
  73    *
  74    * Allocates the internal buffer fallibly.
  75    */
  76   static mozilla::Maybe<Buffer<T>> CopyFrom(mozilla::Span<const T> aSpan) {
  77     auto data = mozilla::MakeUniqueFallible<T[]>(aSpan.Length());
  78     if (!data) {
  79       return mozilla::Nothing();
  80     }
  81     std::copy(aSpan.cbegin(), aSpan.cend(), data.get());
  82     return mozilla::Some(Buffer(std::move(data), aSpan.Length()));
  83   }
  84
  85   /**
  86    * Construct a buffer of requested length.
  87    *
  88    * The contents will be initialized or uninitialized according
  89    * to the behavior of mozilla::MakeUnique<T[]>(aLength) for T.
  90    *
  91    * Allocates the internal buffer infallibly. Use Alloc for fallible
  92    * allocation.
  93    */
  94   explicit Buffer(size_t aLength)
  95       : mData(mozilla::MakeUnique<T[]>(aLength)), mLength(aLength) {}
  96
  97   /**
  98    * Create a new Buffer with an internal buffer of requested length.
  99    *
 100    * The contents will be initialized or uninitialized according to the
 101    * behavior of mozilla::MakeUnique<T[]>(aLength) for T.
 102    *
 103    * Allocates the internal buffer fallibly.
 104    */
 105   static mozilla::Maybe<Buffer<T>> Alloc(size_t aLength) {
 106     auto data = mozilla::MakeUniqueFallible<T[]>(aLength);
 107     if (!data) {
 108       return mozilla::Nothing();
 109     }
 110     return mozilla::Some(Buffer(std::move(data), aLength));
 111   }
 112
 113   mozilla::Span<const T> AsSpan() const {
 114     return mozilla::MakeSpan(mData.get(), mLength);
 115   }
 116   mozilla::Span<T> AsWritableSpan() {
 117     return mozilla::MakeSpan(mData.get(), mLength);
 118   }
 119   operator mozilla::Span<const T>() const { return AsSpan(); }
 120   operator mozilla::Span<T>() { return AsWritableSpan(); }
 121
 122   /**
 123    * Guarantees a non-null and aligned pointer
 124    * even for the zero-length case.
 125    */
 126   T* Elements() { return AsWritableSpan().Elements(); }
 127   size_t Length() const { return mLength; }
 128
 129   T& operator[](size_t aIndex) {
 130     MOZ_ASSERT(aIndex < mLength);
 131     return mData.get()[aIndex];
 132   }
 133
 134   const T& operator[](size_t aIndex) const {
 135     MOZ_ASSERT(aIndex < mLength);
 136     return mData.get()[aIndex];
 137   }
 138
 139   typedef T* iterator;
 140   typedef const T* const_iterator;
 141   typedef ReverseIterator<T*> reverse_iterator;
 142   typedef ReverseIterator<const T*> const_reverse_iterator;
 143
 144   // Methods for range-based for loops.
 145   iterator begin() { return mData.get(); }
 146   const_iterator begin() const { return mData.get(); }
 147   const_iterator cbegin() const { return begin(); }
 148   iterator end() { return mData.get() + mLength; }
 149   const_iterator end() const { return mData.get() + mLength; }
 150   const_iterator cend() const { return end(); }
 151
 152   // Methods for reverse iterating.
 153   reverse_iterator rbegin() { return reverse_iterator(end()); }
 154   const_reverse_iterator rbegin() const {
 155     return const_reverse_iterator(end());
 156   }
 157   const_reverse_iterator crbegin() const { return rbegin(); }
 158   reverse_iterator rend() { return reverse_iterator(begin()); }
 159   const_reverse_iterator rend() const {
 160     return const_reverse_iterator(begin());
 161   }
 162   const_reverse_iterator crend() const { return rend(); }
 163 };
 164
 165 } /* namespace mozilla */
 166
 167 #endif /* mozilla_Buffer_h */