tornavis/source/blender/blenlib/BLI_array.hh

/* SPDX-FileCopyrightText: 2023 Blender Authors
 *
 * SPDX-License-Identifier: GPL-2.0-or-later */

#pragma once

/** \file
 * \ingroup bli
 *
 * A `blender::Array<T>` is a container for a fixed size array the size of which is NOT known at
 * compile time.
 *
 * If the size is known at compile time, `std::array<T, N>` should be used instead.
 *
 * blender::Array should usually be used instead of blender::Vector whenever the number of elements
 * is known at construction time. Note however, that blender::Array will default construct all
 * elements when initialized with the size-constructor. For trivial types, this does nothing. In
 * all other cases, this adds overhead.
 *
 * A main benefit of using Array over Vector is that it expresses the intent of the developer
 * better. It indicates that the size of the data structure is not expected to change. Furthermore,
 * you can be more certain that an array does not over-allocate.
 *
 * blender::Array supports small object optimization to improve performance when the size turns out
 * to be small at run-time.
 */

#include "BLI_allocator.hh"
#include "BLI_index_range.hh"
#include "BLI_memory_utils.hh"
#include "BLI_span.hh"
#include "BLI_utildefines.h"

namespace blender {

template<
    /**
     * The type of the values stored in the array.
     */
    typename T,
    /**
     * The number of values that can be stored in the array, without doing a heap allocation.
     */
    int64_t InlineBufferCapacity = default_inline_buffer_capacity(sizeof(T)),
    /**
     * The allocator used by this array. Should rarely be changed, except when you don't want that
     * MEM_* functions are used internally.
     */
    typename Allocator = GuardedAllocator>
class Array {
 public:
  using value_type = T;
  using pointer = T *;
  using const_pointer = const T *;
  using reference = T &;
  using const_reference = const T &;
  using iterator = T *;
  using const_iterator = const T *;
  using size_type = int64_t;

 private:
  /** The beginning of the array. It might point into the inline buffer. */
  T *data_;

  /** Number of elements in the array. */
  int64_t size_;

  /** Used for allocations when the inline buffer is too small. */
  BLI_NO_UNIQUE_ADDRESS Allocator allocator_;

  /** A placeholder buffer that will remain uninitialized until it is used. */
  BLI_NO_UNIQUE_ADDRESS TypedBuffer<T, InlineBufferCapacity> inline_buffer_;

 public:
  /**
   * By default an empty array is created.
   */
  Array(Allocator allocator = {}) noexcept : allocator_(allocator)
  {
    data_ = inline_buffer_;
    size_ = 0;
  }

  Array(NoExceptConstructor, Allocator allocator = {}) noexcept : Array(allocator) {}

  /**
   * Create a new array that contains copies of all values.
   */
  template<typename U, BLI_ENABLE_IF((std::is_convertible_v<U, T>))>
  Array(Span<U> values, Allocator allocator = {}) : Array(NoExceptConstructor(), allocator)
  {
    const int64_t size = values.size();
    data_ = this->get_buffer_for_size(size);
    uninitialized_convert_n<U, T>(values.data(), size, data_);
    size_ = size;
  }

  /**
   * Create a new array that contains copies of all values.
   */
  template<typename U, BLI_ENABLE_IF((std::is_convertible_v<U, T>))>
  Array(const std::initializer_list<U> &values, Allocator allocator = {})
      : Array(Span<U>(values), allocator)
  {
  }

  Array(const std::initializer_list<T> &values, Allocator allocator = {})
      : Array(Span<T>(values), allocator)
  {
  }

  /**
   * Create a new array with the given size. All values will be default constructed. For trivial
   * types like int, default construction does nothing.
   *
   * We might want another version of this in the future, that does not do default construction
   * even for non-trivial types. This should not be the default though, because one can easily mess
   * up when dealing with uninitialized memory.
   */
  explicit Array(int64_t size, Allocator allocator = {}) : Array(NoExceptConstructor(), allocator)
  {
    data_ = this->get_buffer_for_size(size);
    default_construct_n(data_, size);
    size_ = size;
  }

  /**
   * Create a new array with the given size. All values will be initialized by copying the given
   * default.
   */
  Array(int64_t size, const T &value, Allocator allocator = {})
      : Array(NoExceptConstructor(), allocator)
  {
    BLI_assert(size >= 0);
    data_ = this->get_buffer_for_size(size);
    uninitialized_fill_n(data_, size, value);
    size_ = size;
  }

  /**
   * Create a new array with uninitialized elements. The caller is responsible for constructing the
   * elements. Moving, copying or destructing an Array with uninitialized elements invokes
   * undefined behavior.
   *
   * This should be used very rarely. Note, that the normal size-constructor also does not
   * initialize the elements when T is trivially constructible. Therefore, it only makes sense to
   * use this with non trivially constructible types.
   *
   * Usage:
   *  Array<std::string> my_strings(10, NoInitialization());
   */
  Array(int64_t size, NoInitialization, Allocator allocator = {})
      : Array(NoExceptConstructor(), allocator)
  {
    BLI_assert(size >= 0);
    data_ = this->get_buffer_for_size(size);
    size_ = size;
  }

  Array(const Array &other) : Array(other.as_span(), other.allocator_) {}

  Array(Array &&other) noexcept(std::is_nothrow_move_constructible_v<T>)
      : Array(NoExceptConstructor(), other.allocator_)
  {
    if (other.data_ == other.inline_buffer_) {
      uninitialized_relocate_n(other.data_, other.size_, data_);
    }
    else {
      data_ = other.data_;
    }
    size_ = other.size_;

    other.data_ = other.inline_buffer_;
    other.size_ = 0;
  }

  ~Array()
  {
    destruct_n(data_, size_);
    this->deallocate_if_not_inline(data_);
  }

  Array &operator=(const Array &other)
  {
    return copy_assign_container(*this, other);
  }

  Array &operator=(Array &&other) noexcept(std::is_nothrow_move_constructible_v<T>)
  {
    return move_assign_container(*this, std::move(other));
  }

  T &operator[](int64_t index)
  {
    BLI_assert(index >= 0);
    BLI_assert(index < size_);
    return data_[index];
  }

  const T &operator[](int64_t index) const
  {
    BLI_assert(index >= 0);
    BLI_assert(index < size_);
    return data_[index];
  }

  operator Span<T>() const
  {
    return Span<T>(data_, size_);
  }

  operator MutableSpan<T>()
  {
    return MutableSpan<T>(data_, size_);
  }

  template<typename U, BLI_ENABLE_IF((is_span_convertible_pointer_v<T, U>))>
  operator Span<U>() const
  {
    return Span<U>(data_, size_);
  }

  template<typename U, BLI_ENABLE_IF((is_span_convertible_pointer_v<T, U>))>
  operator MutableSpan<U>()
  {
    return MutableSpan<U>(data_, size_);
  }

  Span<T> as_span() const
  {
    return *this;
  }

  MutableSpan<T> as_mutable_span()
  {
    return *this;
  }

  /**
   * Returns the number of elements in the array.
   */
  int64_t size() const
  {
    return size_;
  }

  /**
   * Returns true when the number of elements in the array is zero.
   */
  bool is_empty() const
  {
    return size_ == 0;
  }

  /**
   * Copies the given value to every element in the array.
   */
  void fill(const T &value) const
  {
    initialized_fill_n(data_, size_, value);
  }

  /**
   * Return a reference to the first element in the array.
   * This invokes undefined behavior when the array is empty.
   */
  const T &first() const
  {
    BLI_assert(size_ > 0);
    return *data_;
  }
  T &first()
  {
    BLI_assert(size_ > 0);
    return *data_;
  }

  /**
   * Return a reference to the nth last element.
   * This invokes undefined behavior when the array is too short.
   */
  const T &last(const int64_t n = 0) const
  {
    BLI_assert(n >= 0);
    BLI_assert(n < size_);
    return *(data_ + size_ - 1 - n);
  }
  T &last(const int64_t n = 0)
  {
    BLI_assert(n >= 0);
    BLI_assert(n < size_);
    return *(data_ + size_ - 1 - n);
  }

  /**
   * Get a pointer to the beginning of the array.
   */
  const T *data() const
  {
    return data_;
  }
  T *data()
  {
    return data_;
  }

  const T *begin() const
  {
    return data_;
  }
  const T *end() const
  {
    return data_ + size_;
  }

  T *begin()
  {
    return data_;
  }
  T *end()
  {
    return data_ + size_;
  }

  std::reverse_iterator<T *> rbegin()
  {
    return std::reverse_iterator<T *>(this->end());
  }
  std::reverse_iterator<T *> rend()
  {
    return std::reverse_iterator<T *>(this->begin());
  }

  std::reverse_iterator<const T *> rbegin() const
  {
    return std::reverse_iterator<T *>(this->end());
  }
  std::reverse_iterator<const T *> rend() const
  {
    return std::reverse_iterator<T *>(this->begin());
  }

  /**
   * Get an index range containing all valid indices for this array.
   */
  IndexRange index_range() const
  {
    return IndexRange(size_);
  }

  /**
   * Sets the size to zero. This should only be used when you have manually destructed all elements
   * in the array beforehand. Use with care.
   */
  void clear_without_destruct()
  {
    size_ = 0;
  }

  /**
   * Access the allocator used by this array.
   */
  Allocator &allocator()
  {
    return allocator_;
  }
  const Allocator &allocator() const
  {
    return allocator_;
  }

  /**
   * Get the value of the InlineBufferCapacity template argument. This is the number of elements
   * that can be stored without doing an allocation.
   */
  static int64_t inline_buffer_capacity()
  {
    return InlineBufferCapacity;
  }

  /**
   * Destruct values and create a new array of the given size. The values in the new array are
   * default constructed.
   */
  void reinitialize(const int64_t new_size)
  {
    BLI_assert(new_size >= 0);
    int64_t old_size = size_;

    destruct_n(data_, size_);
    size_ = 0;

    if (new_size <= old_size) {
      default_construct_n(data_, new_size);
    }
    else {
      T *new_data = this->get_buffer_for_size(new_size);
      try {
        default_construct_n(new_data, new_size);
      }
      catch (...) {
        this->deallocate_if_not_inline(new_data);
        throw;
      }
      this->deallocate_if_not_inline(data_);
      data_ = new_data;
    }

    size_ = new_size;
  }

 private:
  T *get_buffer_for_size(int64_t size)
  {
    if (size <= InlineBufferCapacity) {
      return inline_buffer_;
    }
    else {
      return this->allocate(size);
    }
  }

  T *allocate(int64_t size)
  {
    return static_cast<T *>(allocator_.allocate(size_t(size) * sizeof(T), alignof(T), AT));
  }

  void deallocate_if_not_inline(T *ptr)
  {
    if (ptr != inline_buffer_) {
      allocator_.deallocate(ptr);
    }
  }
};

/**
 * Same as a normal Array, but does not use Blender's guarded allocator. This is useful when
 * allocating memory with static storage duration.
 */
template<typename T, int64_t InlineBufferCapacity = default_inline_buffer_capacity(sizeof(T))>
using RawArray = Array<T, InlineBufferCapacity, RawAllocator>;

}  // namespace blender