[Pitch] `@OptionSet` macro

[esummers (Eric)]

@tera

Interestingly, it is reversed compared to an example in the motivation section of the pitch (not an enum inside a struct but a struct inside an enum).

I wonder if this pitch should change so it could be used in SwiftUI?

This small change would allow it to work both like in the pitch or like in SwiftUI.

// Similar to Edge.Set
enum ShippingOptions: Int {
    case nextDay, secondDay, priority, standard

    @OptionSet<ShippingOptions>
    struct Set { }
}

// Similar to example in pitch
@OptionSet<ShippingOptions.Options>
struct ShippingOptions { 
  private enum Options: Int {
    case nextDay, secondDay, priority, standard
  } 
}

EDIT: Updated to work with enum on outside or inside.