Method borrow

cpp/fory/util/pool.h:60–74

  template <typename Handler>
  auto borrow(Handler &&handler)
      -> decltype(std::forward<Handler>(handler)(std::declval<T &>())) {
    // Provide a convenient scoped access pattern while guaranteeing the object
    // is returned even if the handler throws.
    Ptr item = acquire();
    using ResultType =
        decltype(std::forward<Handler>(handler)(std::declval<T &>()));
    if constexpr (std::is_void_v<ResultType>) {
      std::forward<Handler>(handler)(*item);
      return;
    } else {
      ResultType result = std::forward<Handler>(handler)(*item);
      return result;
    }
  }

private:
  std::unique_ptr<T> acquire_raw() {