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May 29, 2024
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[6.0🍒] Docs: add release note for SE-427 #73950

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35 changes: 35 additions & 0 deletions CHANGELOG.md
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Expand Up @@ -5,6 +5,40 @@

## Swift 6.0

* [SE-0427][]:
You can now suppress `Copyable` on protocols, generic parameters,
and existentials:

```swift
// Protocol does not require conformers to be Copyable.
protocol Flower: ~Copyable {
func bloom()
}

// Noncopyable type
struct Marigold: Flower, ~Copyable {
func bloom() { print("Marigold blooming!") }
}

// Copyable type
struct Hibiscus: Flower {
func bloom() { print("Hibiscus blooming!") }
}

func startSeason(_ flower: borrowing some Flower & ~Copyable) {
flower.bloom()
}

startSeason(Marigold())
startSeason(Hibiscus())
```

By writing `~Copyable` on a generic type, you're suppressing a default
`Copyable` constraint that would otherwise appear on that type. This permits
noncopyable types, which have no `Copyable` conformance, to conform to such
protocols and be substituted for those generic types. Full functionality of this
feature requires the newer Swift 6 runtime.

* Since its introduction in Swift 5.1 the @TaskLocal property wrapper was used to
create and access task-local value bindings. Property wrappers introduce mutable storage,
which was now properly flagged as potential source of concurrency unsafety.
Expand Down Expand Up @@ -10252,6 +10286,7 @@ using the `.dynamicType` member to retrieve the type of an expression should mig
[SE-0412]: https://github.com/apple/swift-evolution/blob/main/proposals/0412-strict-concurrency-for-global-variables.md
[SE-0413]: https://github.com/apple/swift-evolution/blob/main/proposals/0413-typed-throws.md
[SE-0422]: https://github.com/apple/swift-evolution/blob/main/proposals/0422-caller-side-default-argument-macro-expression.md
[SE-0427]: https://github.com/apple/swift-evolution/blob/main/proposals/0427-noncopyable-generics.md
[#64927]: <https://github.com/apple/swift/issues/64927>
[#42697]: <https://github.com/apple/swift/issues/42697>
[#42728]: <https://github.com/apple/swift/issues/42728>
Expand Down