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| 1 /* |
| 2 * Copyright 2015 The WebRTC Project Authors. All rights reserved. |
| 3 * |
| 4 * Use of this source code is governed by a BSD-style license |
| 5 * that can be found in the LICENSE file in the root of the source |
| 6 * tree. An additional intellectual property rights grant can be found |
| 7 * in the file PATENTS. All contributing project authors may |
| 8 * be found in the AUTHORS file in the root of the source tree. |
| 9 */ |
| 10 |
| 11 #ifndef WEBRTC_BASE_ARRAY_VIEW_H_ |
| 12 #define WEBRTC_BASE_ARRAY_VIEW_H_ |
| 13 |
| 14 #include <vector> |
| 15 |
| 16 #include "webrtc/base/checks.h" |
| 17 |
| 18 namespace rtc { |
| 19 |
| 20 // Keeps track of an array (a pointer and a size) that it doesn't own. |
| 21 // ArrayView objects are immutable except for assignment, and small enough to |
| 22 // be cheaply passed by value. |
| 23 // |
| 24 // Note that ArrayView<T> and ArrayView<const T> are distinct types; this is |
| 25 // how you would represent mutable and unmutable views of an array. |
| 26 template <typename T> |
| 27 class ArrayView final { |
| 28 public: |
| 29 // Construct an empty ArrayView. |
| 30 ArrayView() : ArrayView(static_cast<T*>(nullptr), 0) {} |
| 31 |
| 32 // Construct an ArrayView for a (pointer,size) pair. |
| 33 template <typename U> |
| 34 ArrayView(U* data, size_t size) |
| 35 : data_(size == 0 ? nullptr : data), size_(size) { |
| 36 CheckInvariant(); |
| 37 } |
| 38 |
| 39 // Construct an ArrayView for an array. |
| 40 template <typename U, size_t N> |
| 41 ArrayView(U (&array)[N]) : ArrayView(&array[0], N) {} |
| 42 |
| 43 // Construct an ArrayView for any type U that has a size() method whose |
| 44 // return value converts implicitly to size_t, and a data() method whose |
| 45 // return value converts implicitly to T*. In particular, this means we allow |
| 46 // conversion from ArrayView<T> to ArrayView<const T>, but not the other way |
| 47 // around. Other allowed conversions include std::vector<T> to ArrayView<T> |
| 48 // or ArrayView<const T>, const std::vector<T> to ArrayView<const T>, and |
| 49 // rtc::Buffer to ArrayView<uint8_t> (with the same const behavior as |
| 50 // std::vector). |
| 51 template <typename U> |
| 52 ArrayView(U& u) : ArrayView(u.data(), u.size()) {} |
| 53 // TODO(kwiberg): Remove the special case for std::vector (and the include of |
| 54 // <vector>); it is handled by the general case in C++11, since std::vector |
| 55 // has a data() method there. |
| 56 template <typename U> |
| 57 ArrayView(std::vector<U>& u) |
| 58 : ArrayView(u.empty() ? nullptr : &u[0], u.size()) {} |
| 59 |
| 60 // Indexing, size, and iteration. These allow mutation even if the ArrayView |
| 61 // is const, because the ArrayView doesn't own the array. (To prevent |
| 62 // mutation, use ArrayView<const T>.) |
| 63 size_t size() const { return size_; } |
| 64 T* data() const { return data_; } |
| 65 T& operator[](size_t idx) const { |
| 66 RTC_DCHECK_LT(idx, size_); |
| 67 RTC_DCHECK(data_); // Follows from size_ > idx and the class invariant. |
| 68 return data_[idx]; |
| 69 } |
| 70 T* begin() const { return data_; } |
| 71 T* end() const { return data_ + size_; } |
| 72 const T* cbegin() const { return data_; } |
| 73 const T* cend() const { return data_ + size_; } |
| 74 |
| 75 private: |
| 76 // Invariant: !data_ iff size_ == 0. |
| 77 void CheckInvariant() const { RTC_DCHECK_EQ(!data_, size_ == 0); } |
| 78 T* data_; |
| 79 size_t size_; |
| 80 }; |
| 81 |
| 82 } // namespace rtc |
| 83 |
| 84 #endif // WEBRTC_BASE_ARRAY_VIEW_H_ |
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