You can find usages in the GDScript Unirest plugin

This is a fast serializer/deserializer written in GDScript to convert a JSON (Dictionary) to a class, using something similar to the Reflection concecpt. json_to_class can be used to convert a Dictionary to a Class. All keys in the Dictionary will be treated as variables and their types will be guessed in the best way possible. A class (defined by the class_name keyword) must extend Reference or Object or be an inner class, or else Godot will not able to see its properties. It is also possible to deserialize a JSON key to a class property with a different name using the export hint as a variable name.

example usage: