[swift-evolution] Change subscripts to use colons

[James Froggatt]

Subscripts are a hybrid of properties and functions, since they have a parameter list, as well as getters and setters, so use of either symbol will be unusual in this case.

However, I think a colon is more suitable, since it implies the possibility to set the value.


In the future, if we add throwing getters/ setters:

subscript(_ position: Int) -> Element {
    get {
        return …
   }
   throwing set {
        …
    }
}

Should this require ‘throws -> Element’? Using a colon also removes this potentially confusing case.


Thoughts?