Warnings for ambiguous none cases 관련

HACKING WITH SWIFT

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What's new in Swift?

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Warnings for ambiguous none cases | Changes in Swift 5.1

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Warnings for ambiguous none cases

Available from Swift 5.1

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.none'; did you mean 'BorderStyle.none' instead?” This avoids the source compatibility breakage of an error, but at least informs developers that their code might not quite mean what they thought.

Other Changes in Swift 5.1

Improvements to synthesized memberwise initializers | Changes in Swift 5.1

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Improvements to synthesized memberwise initializers

Implicit returns from single-expression functions | Changes in Swift 5.1

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Implicit returns from single-expression functions

Universal Self | Changes in Swift 5.1

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Universal Self

Opaque return types | Changes in Swift 5.1

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Opaque return types

Static and class subscripts | Changes in Swift 5.1

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Static and class subscripts

Matching optional enums against non-optionals | Changes in Swift 5.1

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Matching optional enums against non-optionals

Ordered collection diffing | Changes in Swift 5.1

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Ordered collection diffing

Creating uninitialized arrays | Changes in Swift 5.1

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Creating uninitialized arrays

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