JSON to Dart

Dart has no built-in JSON reflection, so every model class needs fromJson and toJson written by hand. That is a lot of repetitive code for a Flutter app talking to a real API, and this generates all of it.

Every nested object gets its own class with its own pair of methods, so decoding a payload leaves you holding typed models rather than a raw Map<String, dynamic> you have to keep casting.

Are the fields immutable?

Yes. Fields are final with a const constructor and named required parameters, which is the conventional shape for a Flutter model and lets the widget tree treat instances as values.

Why hand-written fromJson instead of json_serializable?

Generated code needs build_runner in the project and a part file next to the class, neither of which exists when you are pasting a model into a scratch file. The methods here are complete as written — no build step, nothing to generate.

How are optional fields decided?

Every record in an array is inspected, not just the first. A field that appears in some records and not others is typed as optional, and a value that is sometimes null widens accordingly. Generators that read only the first element get this wrong on exactly the payloads where it matters.

What happens to a key that is a reserved word?

It is renamed to something legal in the target language, and where the language supports it, an annotation records the original JSON key so serialisation still round-trips.