You can provide alternative collections if needed by templating basic_json; std::map is just a default. Personally I like using a flat_map which is an ordered m

You can provide alternative collections if needed by templating basic_json; std::map is just a default. Personally I like using a flat_map which is an ordered map built on top of a vector, which provides nice cache locality and is generally even faster than a hash map / unordered_map except for extremely large objects.