libartbase/base/array_ref.h

/*
 * Copyright (C) 2014 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#ifndef ART_LIBARTBASE_BASE_ARRAY_REF_H_
#define ART_LIBARTBASE_BASE_ARRAY_REF_H_

#include <type_traits>
#include <vector>

#include <android-base/logging.h>

namespace art {

/**
 * @brief A container that references an array.
 *
 * @details The template class ArrayRef provides a container that references
 * an external array. This external array must remain alive while the ArrayRef
 * object is in use. The external array may be a std::vector<>-backed storage
 * or any other contiguous chunk of memory but that memory must remain valid,
 * i.e. the std::vector<> must not be resized for example.
 *
 * Except for copy/assign and insert/erase/capacity functions, the interface
 * is essentially the same as std::vector<>. Since we don't want to throw
 * exceptions, at() is also excluded.
 */
template <typename T>
class ArrayRef {
 public:
  using value_type = T;
  using reference = T&;
  using const_reference = const T&;
  using pointer = T*;
  using const_pointer = const T*;
  using iterator = T*;
  using const_iterator = const T*;
  using reverse_iterator = std::reverse_iterator<iterator>;
  using const_reverse_iterator = std::reverse_iterator<const_iterator>;
  using difference_type = ptrdiff_t;
  using size_type = size_t;

  // Constructors.

  constexpr ArrayRef()
      : array_(nullptr), size_(0u) {
  }

  template <size_t size>
  explicit constexpr ArrayRef(T (&array)[size])
      : array_(array), size_(size) {
  }

  template <typename U,
            size_t size,
            typename = std::enable_if_t<std::is_same_v<T, const U>>>
  explicit constexpr ArrayRef(U (&array)[size])
      : array_(array), size_(size) {
  }

  constexpr ArrayRef(T* array, size_t size)
      : array_(array), size_(size) {
  }

  template <typename Vector,
            typename = std::enable_if_t<std::is_same_v<typename Vector::value_type, value_type>>>
  explicit ArrayRef(Vector& v)
      : array_(v.data()), size_(v.size()) {
  }

  template <typename Vector,
            typename = std::enable_if_t<
                std::is_same_v<std::add_const_t<typename Vector::value_type>, value_type>>>
  explicit ArrayRef(const Vector& v)
      : array_(v.data()), size_(v.size()) {
  }

  ArrayRef(const ArrayRef&) = default;

  // Assignment operators.

  ArrayRef& operator=(const ArrayRef& other) {
    array_ = other.array_;
    size_ = other.size_;
    return *this;
  }

  template <typename U>
  std::enable_if_t<std::is_same_v<T, const U>, ArrayRef>&
  operator=(const ArrayRef<U>& other) {
    return *this = ArrayRef(other);
  }

  template <typename U>
  static ArrayRef Cast(const ArrayRef<U>& src) {
    return ArrayRef(reinterpret_cast<const T*>(src.data()),
                    src.size() * sizeof(T) / sizeof(U));
  }

  // Destructor.
  ~ArrayRef() = default;

  // Iterators.
  iterator begin() { return array_; }
  const_iterator begin() const { return array_; }
  const_iterator cbegin() const { return array_; }
  iterator end() { return array_ + size_; }
  const_iterator end() const { return array_ + size_; }
  const_iterator cend() const { return array_ + size_; }
  reverse_iterator rbegin() { return reverse_iterator(end()); }
  const_reverse_iterator rbegin() const { return const_reverse_iterator(end()); }
  const_reverse_iterator crbegin() const { return const_reverse_iterator(cend()); }
  reverse_iterator rend() { return reverse_iterator(begin()); }
  const_reverse_iterator rend() const { return const_reverse_iterator(begin()); }
  const_reverse_iterator crend() const { return const_reverse_iterator(cbegin()); }

  // Size.
  size_type size() const { return size_; }
  bool empty() const { return size() == 0u; }

  // Element access. NOTE: Not providing at().

  reference operator[](size_type n) {
    DCHECK_LT(n, size_);
    return array_[n];
  }

  const_reference operator[](size_type n) const {
    DCHECK_LT(n, size_);
    return array_[n];
  }

  reference front() {
    DCHECK(!empty());
    return array_[0];
  }

  const_reference front() const {
    DCHECK(!empty());
    return array_[0];
  }

  reference back() {
    DCHECK(!empty());
    return array_[size_ - 1u];
  }

  const_reference back() const {
    DCHECK(!empty());
    return array_[size_ - 1u];
  }

  value_type* data() { return array_; }
  const value_type* data() const { return array_; }

  ArrayRef SubArray(size_type pos) {
    return SubArray(pos, size() - pos);
  }

  ArrayRef<const T> SubArray(size_type pos) const {
    return SubArray(pos, size() - pos);
  }

  ArrayRef SubArray(size_type pos, size_type length) {
    DCHECK_LE(pos, size());
    DCHECK_LE(length, size() - pos);
    return ArrayRef(data() + pos, length);
  }

  ArrayRef<const T> SubArray(size_type pos, size_type length) const {
    DCHECK_LE(pos, size());
    DCHECK_LE(length, size() - pos);
    return ArrayRef<const T>(data() + pos, length);
  }

 private:
  T* array_;
  size_t size_;
};

template <typename T>
bool operator==(const ArrayRef<T>& lhs, const ArrayRef<T>& rhs) {
  return lhs.size() == rhs.size() && std::equal(lhs.begin(), lhs.end(), rhs.begin());
}

template <typename T>
bool operator!=(const ArrayRef<T>& lhs, const ArrayRef<T>& rhs) {
  return !(lhs == rhs);
}

template<typename T>
std::ostream& operator<<(std::ostream& os, const ArrayRef<T>& ts) {
  bool first = true;
  os << "[";
  for (const T& t : ts) {
    if (!first) { os << ", "; }
    first = false;
    os << t;
  }
  os << "]";
  return os;
}

}  // namespace art


#endif  // ART_LIBARTBASE_BASE_ARRAY_REF_H_