Feature Request: "reserve" method for arrays

[moellerm4d]

Hi!

It would be nice to have a "reserve" method for arrays. It can help improve Speed.

For test purposes i added to v3.11.3:

inline void nlohmann:json_abi_v3_11_3::basic_ison<...>::reserve(size_t count)

It looks like this:

    /// @brief reserve element memory for array
    void reserve(size_t count)
    {
        // reserve only for arrays
        if (JSON_HEDLEY_LIKELY(is_array()))
        {
            // reserve requested count
            m_data.m_value.array->reserve(count);
            return;
        }

        JSON_THROW(type_error::create(309, detail::concat("cannot use reserve() with ", type_name()), this));
    }

And it can be used like this:

        auto js_array(json::array());
        js_array.reserve(1'000);

I would appreciate if this could be added to the lib. I looked in the code and tried to search issues and discussions but could not find anything like it. ...which might be due to my skills...

Thanks!

[gregmarr]

Here's how to do it.

int main() {
  auto js_array(nlohmann::json::array());
  if (js_array.is_array())
    js_array.get_ref<nlohmann::json::array_t&>().reserve(1000);
  return 0;
}