How does the immutable annotation work in Dart?

Question

How does the @immutable annotation work?

I learned annotations are related to meta and reflection recently.

However, I cannot find the source code it proves.

Please tell me how to work or the source code.

Answer 1

Annotations by themselves don't do anything. If you look at the source code for an annotation such as Immutable, it's not very interesting. Annotations are just special tags that live in the source code; they don't affect the compiled code.

An annotation usually must work in tandem with some tool that does static analysis of your code and that looks for that annotation. In the case of @immutable, that's handled by Dart's static analyzer when you run dart analyze. (Other packages might provide their own annotations that are handled by other tools; for example, package:mockito has @GenerateNiceMocks/@GenerateMocks annotations that are processed when you run its build-runner step.)

It looks like the analyzer handles @immutable in its internal _checkForImmutable function.