extract sub key data without iterating

[JGriff-dev]

I'm new to nlohmann json and I would first like to congratulate the developer on the best JSON library I've seen, its great!

I've looked for and seen requests for multiple key type functionality, which is something I use a lot. Where a hierarchical object structure is known, accessing it easily & safely can be tedious. I discovered today a very simple way of doing this with this library which I think would merit adding to the documentation. I parse an incoming JSON string containing and object and can extract an array of double values in a sub key using this straight forward method:-

json jData = json::parse(JSON_String);

if (jData["DATA"]["Temperature"].is_array())
{
    std::list<double> dCentigrade =jData["DATA"]["Temperature"];
}

Very simple & safe without having to iterate though each layer of the JSON. The same "is_xxxxxxx()" method can be used to verify any known sub key.

Thanks
John.