[swift-evolution] Adding custom attributes

[Radosław Smogura]

Hello Swift Team,

As it’s my first post on this mailing list, let me introduce my self. My name is Radek Smogura, and for 10 year I work as developer, mainly Java and I know C and C++. I would like to join Swift community and work on Swift language. Previously for hobby I  added properties syntax to it and full closure support (you can find it here https://bitbucket.org/radoslaw_smogura/java-closures-silver-jdk9-langtools/wiki/Home).

I would like to propose custom attributes support, as it would make Swift more robust language, by allowing dependency injection and managed objects (ie. for Core Data or some trivial example like defining JSON structures for REST). I would as well to contribute to this feature to Swift language if possible as fork or branch.

My general high level plan is as follow:
- add experimental feature switch to add parsing custom attributes,
- define and implement attribute syntax,
- compile attributes and store those,
- add validation and compilation to attribute declarations
- - (optionally) refactor current code
- enjoy.

Waiting for your thoughts,
Radek