JsonVariant with .to<JsonArray>(); about arduinojson HOT 1 CLOSED

Hi @EvEggelen,

Thank you for this question.

In the documentation, I forgot to mention that JsonVariant::to<T>() is a no-op if the JsonVariant is unbound. Indeed, you cannot modify a value if there is no value to begin with.

In your case, outputDoc["images"] returns an unbound JsonVariant because there is no "images" member in outputDoc. Returning a bound JsonVariant would require adding the "images" member in outputDoc, which is not what people expect from JsonVariant test = outputDoc["images"].

outputDoc["images"].to<JsonArray>() works because it calls MemberProxy::to<T>(), which knows it must add the member if it's missing. MemberProxy is part of ArduinoJson's internal sauce, so I don't recommend using it in your app.

If you need a bound JsonVariant, you must initialize it with to<JsonVariant>():

- JsonVariant test = outputDoc["images"];
+ JsonVariant test = outputDoc["images"].to<JsonVariant>();
  JsonArray outputlist = test.to<JsonArray>();

This feature is not new to ArduinoJson 7; it was already like that in version 6.

Best regards,
Benoit

from arduinojson.