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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Other changes in Swift 5.1…
- Improvements to synthesized memberwise initializers
- Implicit returns from single-expression functions
- Universal Self
- Opaque return types
- Static and class subscripts
- Matching optional enums against non-optionals
- Ordered collection diffing
- Creating uninitialized arrays
Download all Swift 5.1 changes as a playground Link to Swift 5.1 changes
