How to create annotations and get them in scala

Question

I want to define some annotations and use them in Scala.

I looked into the source of Scala, found in scala.annotation package, there are some annotation

Answer 1

You can find a nice description of how annotations are to be used in Scala in Programming Scala.

So you can define or use annotations in scala. However there is at least one limitation:

Runtime retention is not quite possible. In theory you should subclass ClassFileAnnotation to achieve this, but currently scalac reports the following warning if you do it:

"implementation restriction: subclassing Classfile does not make your annotation visible at runtime. If that is what you want, you must write the annotation class in Java."

It also means that your code is fine as it is (at least as fine as it is currently possible in Scala), but the annotation is on the class only during compile time. So you could use it e.g. in compiler plugins, but you will not be able to access it runtime.