storage.h

// Copyright 2025 The Pigweed Authors
//
// 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
//
//     https://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.
#pragma once
 
#include <array>
 
#include "pw_containers/algorithm.h"
 
namespace pw::containers {
 
 
template <size_t kAlignment, size_t kSizeBytes>
class Storage {
 public:
  using value_type = std::byte;
  using size_type = size_t;
  using pointer = value_type*;
  using const_pointer = const value_type*;
 
  constexpr Storage() : buffer_{} {}
 
  Storage(const Storage&) = delete;
  Storage& operator=(const Storage&) = delete;
 
  Storage(Storage&&) = delete;
  Storage& operator=(Storage&&) = delete;
 
  constexpr pointer data() { return buffer_.data(); }
  constexpr const_pointer data() const { return buffer_.data(); }
 
  constexpr size_type size() const { return buffer_.size(); }
 
  [[nodiscard]] constexpr bool empty() const { return buffer_.empty(); }
 
  constexpr void fill(std::byte value) {
    pw::fill_n(buffer_.data(), buffer_.size(), value);
  }
 
 private:
  alignas(kAlignment) std::array<std::byte, kSizeBytes> buffer_;
};
 
template <typename T, size_t kCount = 1>
using StorageFor = Storage<alignof(T), sizeof(T) * kCount>;
 
inline constexpr size_t kExternalStorage = static_cast<size_t>(-1);
 
 
namespace internal {
 
// Storage wrappers to be used as bases when implementing a container that
// combines a non-owning container with its buffer. These types have to be the
// first base so the storage outlives the container using it.
template <typename T, size_t kCapacity>
struct ArrayStorage {
  StorageFor<T, kCapacity> storage_array;
};
 
}  // namespace internal
}  // namespace pw::containers