Class Arena

include/jwt/stack_alloc.hpp:46–132

  size_t alignment = alignof(std::max_align_t)
>
class Arena
{
public: // 'tors
  Arena() noexcept
    : ptr_(buf_)
  {
    static_assert (alignment <= alignof(std::max_align_t),
        "Alignment chosen is more than the maximum supported alignment");
  }

  /// Non copyable and assignable
  Arena(const Arena&) = delete;
  Arena& operator=(const Arena&) = delete;

  ~Arena() 
  { 
    ptr_ = nullptr; 
  }

public: // Public APIs

  /*
   * Reserves space within the buffer of size atleast 'n'
   * bytes.
   * More bytes maybe reserved based on the alignment requirements.
   *
   * Returns:
   * 1. The pointer within the storage buffer where the object can be constructed.
   * 2. nullptr if space cannot be reserved for requested number of bytes 
   *    (+ alignment padding if applicable)
   */
  template <
    /// The requested alignment for this allocation.
    /// Must be less than or equal to the 'alignment'.
    size_t requested_alignment
  >
  char* allocate(size_t n) noexcept;

  /*
   * Free back the space pointed by p within the storage buffer.
   */
  void deallocate(char* p, size_t n) noexcept;

  /*
   * The size of the internal storage buffer.
   */
  constexpr static size_t size() noexcept
  {
    return N;
  }

  /*
   * Returns number of remaining bytes within the storage buffer
   * that can be used for further allocation requests.
   */
  size_t used() const noexcept
  {
    return static_cast<size_t>(ptr_ - buf_);