Read NSHipster’s Swift Property Wrappers. Despite useful info on topic this post has chart showing connection between protocols and structs conforming to them which define number types in Swift. Same about String and Substring. This information is difficult to find anywhere else. I like this conclusion in post because I find myself feeling the same:

Swift is a much, much more complex language than Objective-C. That’s been true since Swift 1.0 and has only become more so over time.

Read with joy NSHipster’s Exhaustive rundown of the many faces of @.

Jumped to Attributes of Swift language reference.