Swift’s optionals are implemented as an enum of two cases: some
and none
. This gave rise to the possibility of confusion if we created our own enums that had a none
case, then wrapped that inside an optional.
For example:
enum BorderStyle {
case none
case solid(thickness: Int)
}
Used as a non-optional this was always clear:
let border1: BorderStyle = .none
print(border1)
That will print “none”. But if we used an optional for that enum – if we didn’t know what border style to use – then we’d hit problems:
let border2: BorderStyle? = .none
print(border2)
That prints “nil”, because Swift assumes .none
means the optional is empty, rather than an optional with the value BorderStyle.none
.
In Swift 5.1 this confusion now prints a warning: “Assuming you mean 'Optional
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