336 lines
13 KiB
C++
336 lines
13 KiB
C++
/*
|
|
* 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.
|
|
*/
|
|
|
|
#ifndef API_ARRAY_VIEW_H_
|
|
#define API_ARRAY_VIEW_H_
|
|
|
|
#include <algorithm>
|
|
#include <array>
|
|
#include <cstddef>
|
|
#include <iterator>
|
|
#include <type_traits>
|
|
|
|
#include "rtc_base/checks.h"
|
|
#include "rtc_base/type_traits.h"
|
|
|
|
namespace rtc {
|
|
|
|
// tl;dr: rtc::ArrayView is the same thing as gsl::span from the Guideline
|
|
// Support Library.
|
|
//
|
|
// 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 array_view_internal {
|
|
|
|
// 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, array_view_internal::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 array_view_internal
|
|
|
|
template <typename T,
|
|
std::ptrdiff_t Size = array_view_internal::kArrayViewVarSize>
|
|
class ArrayView final : public array_view_internal::ArrayViewBase<T, Size> {
|
|
public:
|
|
using value_type = T;
|
|
using reference = value_type&;
|
|
using const_reference = const value_type&;
|
|
using pointer = value_type*;
|
|
using const_pointer = const value_type*;
|
|
using const_iterator = const T*;
|
|
|
|
// Construct an ArrayView from a pointer and a length.
|
|
template <typename U>
|
|
ArrayView(U* data, size_t size)
|
|
: array_view_internal::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) // NOLINT
|
|
: ArrayView() {}
|
|
ArrayView(std::nullptr_t, size_t size)
|
|
: ArrayView(static_cast<T*>(nullptr), size) {
|
|
static_assert(Size == 0 || Size == array_view_internal::kArrayViewVarSize,
|
|
"");
|
|
RTC_DCHECK_EQ(0, size);
|
|
}
|
|
|
|
// Construct an ArrayView from a C-style array.
|
|
template <typename U, size_t N>
|
|
ArrayView(U (&array)[N]) // NOLINT
|
|
: ArrayView(array, N) {
|
|
static_assert(Size == N || Size == array_view_internal::kArrayViewVarSize,
|
|
"Array size must match ArrayView size");
|
|
}
|
|
|
|
// (Only if size is fixed.) Construct a fixed size ArrayView<T, N> from a
|
|
// non-const std::array instance. For an ArrayView with variable size, the
|
|
// used ctor is ArrayView(U& u) instead.
|
|
template <typename U,
|
|
size_t N,
|
|
typename std::enable_if<
|
|
Size == static_cast<std::ptrdiff_t>(N)>::type* = nullptr>
|
|
ArrayView(std::array<U, N>& u) // NOLINT
|
|
: ArrayView(u.data(), u.size()) {}
|
|
|
|
// (Only if size is fixed.) Construct a fixed size ArrayView<T, N> where T is
|
|
// const from a const(expr) std::array instance. For an ArrayView with
|
|
// variable size, the used ctor is ArrayView(U& u) instead.
|
|
template <typename U,
|
|
size_t N,
|
|
typename std::enable_if<
|
|
Size == static_cast<std::ptrdiff_t>(N)>::type* = nullptr>
|
|
ArrayView(const std::array<U, N>& u) // NOLINT
|
|
: ArrayView(u.data(), u.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 != array_view_internal::kArrayViewVarSize &&
|
|
HasDataAndSize<U, T>::value>::type* = nullptr>
|
|
ArrayView(U& u) // NOLINT
|
|
: ArrayView(u.data(), u.size()) {
|
|
static_assert(U::size() == Size, "Sizes must match exactly");
|
|
}
|
|
template <
|
|
typename U,
|
|
typename std::enable_if<Size != array_view_internal::kArrayViewVarSize &&
|
|
HasDataAndSize<U, T>::value>::type* = nullptr>
|
|
ArrayView(const U& u) // NOLINT(runtime/explicit)
|
|
: 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 == array_view_internal::kArrayViewVarSize &&
|
|
HasDataAndSize<U, T>::value>::type* = nullptr>
|
|
ArrayView(U& u) // NOLINT
|
|
: ArrayView(u.data(), u.size()) {}
|
|
template <
|
|
typename U,
|
|
typename std::enable_if<Size == array_view_internal::kArrayViewVarSize &&
|
|
HasDataAndSize<U, T>::value>::type* = nullptr>
|
|
ArrayView(const U& u) // NOLINT(runtime/explicit)
|
|
: 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(); }
|
|
std::reverse_iterator<T*> rbegin() const {
|
|
return std::make_reverse_iterator(end());
|
|
}
|
|
std::reverse_iterator<T*> rend() const {
|
|
return std::make_reverse_iterator(begin());
|
|
}
|
|
std::reverse_iterator<const T*> crbegin() const {
|
|
return std::make_reverse_iterator(cend());
|
|
}
|
|
std::reverse_iterator<const T*> crend() const {
|
|
return std::make_reverse_iterator(cbegin());
|
|
}
|
|
|
|
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);
|
|
}
|
|
|
|
// Only for primitive types that have the same size and aligment.
|
|
// Allow reinterpret cast of the array view to another primitive type of the
|
|
// same size.
|
|
// Template arguments order is (U, T, Size) to allow deduction of the template
|
|
// arguments in client calls: reinterpret_array_view<target_type>(array_view).
|
|
template <typename U, typename T, std::ptrdiff_t Size>
|
|
inline ArrayView<U, Size> reinterpret_array_view(ArrayView<T, Size> view) {
|
|
static_assert(sizeof(U) == sizeof(T) && alignof(U) == alignof(T),
|
|
"ArrayView reinterpret_cast is only supported for casting "
|
|
"between views that represent the same chunk of memory.");
|
|
static_assert(
|
|
std::is_fundamental<T>::value && std::is_fundamental<U>::value,
|
|
"ArrayView reinterpret_cast is only supported for casting between "
|
|
"fundamental types.");
|
|
return ArrayView<U, Size>(reinterpret_cast<U*>(view.data()), view.size());
|
|
}
|
|
|
|
} // namespace rtc
|
|
|
|
#endif // API_ARRAY_VIEW_H_
|