Why scala people don't like annotation?

Question

Attribute in .NET is a very popular feature. And Java added Annotation after 1.5 Annotations are used everywhere, see Java EE and Spring. But few scala library use annotation. l

Answer 1

You've pretty much answered your own question when you said that they're used for compiler magic. For the other uses it's usually some kind of runtime magic, where the two main tools are reflection and byte code transformation.

For the JSON case, the choices for the conversion would be the following: 1. A function or class that parses your JValue and builds your class T. 2. Reflection over the target classes to determine their layout and what is optional, then some "dynamic" code which runs over that parsed data to create and then eventually cast to the appropriate type.