Move array_view.h to webrtc/api/

webrtc/rtc_base/array_view.h

 /*
  *  Copyright 2015 The WebRTC Project Authors. All rights reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
+// This header is for backwards compatibility only, and will be removed soon.
+// Include webrtc/api/array_view.h instead.
+
 #ifndef WEBRTC_RTC_BASE_ARRAY_VIEW_H_
 #define WEBRTC_RTC_BASE_ARRAY_VIEW_H_
 
-#include "webrtc/rtc_base/checks.h"
-#include "webrtc/rtc_base/type_traits.h"
-
-namespace rtc {
-
-// Many functions read from or write to arrays. The obvious way to do this is
-// to use two arguments, a pointer to the first element and an element count:
-//
-//   bool Contains17(const int* arr, size_t size) {
-//     for (size_t i = 0; i < size; ++i) {
-//       if (arr[i] == 17)
-//         return true;
-//     }
-//     return false;
-//   }
-//
-// This is flexible, since it doesn't matter how the array is stored (C array,
-// std::vector, rtc::Buffer, ...), but it's error-prone because the caller has
-// to correctly specify the array length:
-//
-//   Contains17(arr, arraysize(arr));     // C array
-//   Contains17(arr.data(), arr.size());  // std::vector
-//   Contains17(arr, size);               // pointer + size
-//   ...
-//
-// It's also kind of messy to have two separate arguments for what is
-// conceptually a single thing.
-//
-// Enter rtc::ArrayView<T>. It contains a T pointer (to an array it doesn't
-// own) and a count, and supports the basic things you'd expect, such as
-// indexing and iteration. It allows us to write our function like this:
-//
-//   bool Contains17(rtc::ArrayView<const int> arr) {
-//     for (auto e : arr) {
-//       if (e == 17)
-//         return true;
-//     }
-//     return false;
-//   }
-//
-// And even better, because a bunch of things will implicitly convert to
-// ArrayView, we can call it like this:
-//
-//   Contains17(arr);                             // C array
-//   Contains17(arr);                             // std::vector
-//   Contains17(rtc::ArrayView<int>(arr, size));  // pointer + size
-//   Contains17(nullptr);                         // nullptr -> empty ArrayView
-//   ...
-//
-// ArrayView<T> stores both a pointer and a size, but you may also use
-// ArrayView<T, N>, which has a size that's fixed at compile time (which means
-// it only has to store the pointer).
-//
-// One important point is that ArrayView<T> and ArrayView<const T> are
-// different types, which allow and don't allow mutation of the array elements,
-// respectively. The implicit conversions work just like you'd hope, so that
-// e.g. vector<int> will convert to either ArrayView<int> or ArrayView<const
-// int>, but const vector<int> will convert only to ArrayView<const int>.
-// (ArrayView itself can be the source type in such conversions, so
-// ArrayView<int> will convert to ArrayView<const int>.)
-//
-// Note: ArrayView is tiny (just a pointer and a count if variable-sized, just
-// a pointer if fix-sized) and trivially copyable, so it's probably cheaper to
-// pass it by value than by const reference.
-
-namespace impl {
-
-// Magic constant for indicating that the size of an ArrayView is variable
-// instead of fixed.
-enum : std::ptrdiff_t { kArrayViewVarSize = -4711 };
-
-// Base class for ArrayViews of fixed nonzero size.
-template <typename T, std::ptrdiff_t Size>
-class ArrayViewBase {
-  static_assert(Size > 0, "ArrayView size must be variable or non-negative");
-
- public:
-  ArrayViewBase(T* data, size_t size) : data_(data) {}
-
-  static constexpr size_t size() { return Size; }
-  static constexpr bool empty() { return false; }
-  T* data() const { return data_; }
-
- protected:
-  static constexpr bool fixed_size() { return true; }
-
- private:
-  T* data_;
-};
-
-// Specialized base class for ArrayViews of fixed zero size.
-template <typename T>
-class ArrayViewBase<T, 0> {
- public:
-  explicit ArrayViewBase(T* data, size_t size) {}
-
-  static constexpr size_t size() { return 0; }
-  static constexpr bool empty() { return true; }
-  T* data() const { return nullptr; }
-
- protected:
-  static constexpr bool fixed_size() { return true; }
-};
-
-// Specialized base class for ArrayViews of variable size.
-template <typename T>
-class ArrayViewBase<T, impl::kArrayViewVarSize> {
- public:
-  ArrayViewBase(T* data, size_t size)
-      : data_(size == 0 ? nullptr : data), size_(size) {}
-
-  size_t size() const { return size_; }
-  bool empty() const { return size_ == 0; }
-  T* data() const { return data_; }
-
- protected:
-  static constexpr bool fixed_size() { return false; }
-
- private:
-  T* data_;
-  size_t size_;
-};
-
-}  // namespace impl
-
-template <typename T, std::ptrdiff_t Size = impl::kArrayViewVarSize>
-class ArrayView final : public impl::ArrayViewBase<T, Size> {
- public:
-  using value_type = T;
-  using const_iterator = const T*;
-
-  // Construct an ArrayView from a pointer and a length.
-  template <typename U>
-  ArrayView(U* data, size_t size)
-      : impl::ArrayViewBase<T, Size>::ArrayViewBase(data, size) {
-    RTC_DCHECK_EQ(size == 0 ? nullptr : data, this->data());
-    RTC_DCHECK_EQ(size, this->size());
-    RTC_DCHECK_EQ(!this->data(),
-                  this->size() == 0);  // data is null iff size == 0.
-  }
-
-  // Construct an empty ArrayView. Note that fixed-size ArrayViews of size > 0
-  // cannot be empty.
-  ArrayView() : ArrayView(nullptr, 0) {}
-  ArrayView(std::nullptr_t) : ArrayView() {}
-  ArrayView(std::nullptr_t, size_t size)
-      : ArrayView(static_cast<T*>(nullptr), size) {
-    static_assert(Size == 0 || Size == impl::kArrayViewVarSize, "");
-    RTC_DCHECK_EQ(0, size);
-  }
-
-  // Construct an ArrayView from an array.
-  template <typename U, size_t N>
-  ArrayView(U (&array)[N]) : ArrayView(array, N) {
-    static_assert(Size == N || Size == impl::kArrayViewVarSize,
-                  "Array size must match ArrayView size");
-  }
-
-  // (Only if size is fixed.) Construct an ArrayView from any type U that has a
-  // static constexpr size() method whose return value is equal to Size, and a
-  // data() method whose return value converts implicitly to T*. In particular,
-  // this means we allow conversion from ArrayView<T, N> to ArrayView<const T,
-  // N>, but not the other way around. We also don't allow conversion from
-  // ArrayView<T> to ArrayView<T, N>, or from ArrayView<T, M> to ArrayView<T,
-  // N> when M != N.
-  template <typename U,
-            typename std::enable_if<
-                Size != impl::kArrayViewVarSize &&
-                HasDataAndSize<U, T>::value>::type* = nullptr>
-  ArrayView(U& u) : ArrayView(u.data(), u.size()) {
-    static_assert(U::size() == Size, "Sizes must match exactly");
-  }
-
-  // (Only if size is variable.) Construct an ArrayView from any type U that
-  // has a size() method whose return value converts implicitly to size_t, and
-  // a data() method whose return value converts implicitly to T*. In
-  // particular, this means we allow conversion from ArrayView<T> to
-  // ArrayView<const T>, but not the other way around. Other allowed
-  // conversions include
-  // ArrayView<T, N> to ArrayView<T> or ArrayView<const T>,
-  // std::vector<T> to ArrayView<T> or ArrayView<const T>,
-  // const std::vector<T> to ArrayView<const T>,
-  // rtc::Buffer to ArrayView<uint8_t> or ArrayView<const uint8_t>, and
-  // const rtc::Buffer to ArrayView<const uint8_t>.
-  template <
-      typename U,
-      typename std::enable_if<Size == impl::kArrayViewVarSize &&
-                              HasDataAndSize<U, T>::value>::type* = nullptr>
-  ArrayView(U& u) : ArrayView(u.data(), u.size()) {}
-
-  // Indexing and iteration. These allow mutation even if the ArrayView is
-  // const, because the ArrayView doesn't own the array. (To prevent mutation,
-  // use a const element type.)
-  T& operator[](size_t idx) const {
-    RTC_DCHECK_LT(idx, this->size());
-    RTC_DCHECK(this->data());
-    return this->data()[idx];
-  }
-  T* begin() const { return this->data(); }
-  T* end() const { return this->data() + this->size(); }
-  const T* cbegin() const { return this->data(); }
-  const T* cend() const { return this->data() + this->size(); }
-
-  ArrayView<T> subview(size_t offset, size_t size) const {
-    return offset < this->size()
-               ? ArrayView<T>(this->data() + offset,
-                              std::min(size, this->size() - offset))
-               : ArrayView<T>();
-  }
-  ArrayView<T> subview(size_t offset) const {
-    return subview(offset, this->size());
-  }
-};
-
-// Comparing two ArrayViews compares their (pointer,size) pairs; it does *not*
-// dereference the pointers.
-template <typename T, std::ptrdiff_t Size1, std::ptrdiff_t Size2>
-bool operator==(const ArrayView<T, Size1>& a, const ArrayView<T, Size2>& b) {
-  return a.data() == b.data() && a.size() == b.size();
-}
-template <typename T, std::ptrdiff_t Size1, std::ptrdiff_t Size2>
-bool operator!=(const ArrayView<T, Size1>& a, const ArrayView<T, Size2>& b) {
-  return !(a == b);
-}
-
-// Variable-size ArrayViews are the size of two pointers; fixed-size ArrayViews
-// are the size of one pointer. (And as a special case, fixed-size ArrayViews
-// of size 0 require no storage.)
-static_assert(sizeof(ArrayView<int>) == 2 * sizeof(int*), "");
-static_assert(sizeof(ArrayView<int, 17>) == sizeof(int*), "");
-static_assert(std::is_empty<ArrayView<int, 0>>::value, "");
-
-template <typename T>
-inline ArrayView<T> MakeArrayView(T* data, size_t size) {
-  return ArrayView<T>(data, size);
-}
-
-}  // namespace rtc
+#include "webrtc/api/array_view.h"
 
 #endif  // WEBRTC_RTC_BASE_ARRAY_VIEW_H_