fixed (pmr) vector by fixed-size allocator

fixed_vector.hh

template <class T, size_t N> struct limited_allocator : std::allocator<T> {
  using value_type = typename std::allocator<T>::value_type;
  using size_type = typename std::allocator<T>::size_type;
  size_type max_size() const noexcept { return N; }
  template <class Other> struct rebind {
    typedef limited_allocator<Other, N> other;
  };

  // make msvc happy
  template <class Other, size_t M> constexpr operator limited_allocator<Other, M>() const noexcept {
    return limited_allocator<Other, M>();
  }
};

template <class T, size_t N> struct limited_pmr_allocator : std::pmr::polymorphic_allocator<T> {
  using value_type = typename std::pmr::polymorphic_allocator<T>::value_type;
  using size_type = typename std::allocator_traits<std::pmr::polymorphic_allocator<T>>::size_type;
  size_type max_size() const noexcept { return N; }
  template <class Other> struct rebind {
    typedef limited_pmr_allocator<Other, N> other;
  };

  template <class Other, size_t M> constexpr operator limited_pmr_allocator<Other, M>() const noexcept {
    return limited_pmr_allocator<Other, M>{this->resource()};
  }
};

template <class T, size_t N> using limited_vector = std::vector<T, limited_allocator<T, N>>;
template <class T, size_t N> using limited_pmr_vector = std::vector<T, limited_pmr_allocator<T, N>>;