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32ec5a61b7
Also make the titles and one line summaries a little more consistent (at least for diagnsotic groups and upcoming language features, haven't gone through the educational notes).
48 lines
1.3 KiB
Markdown
48 lines
1.3 KiB
Markdown
# Existential any (ExistentialAny)
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`any` existential type syntax.
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## Overview
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`any` was introduced in Swift 5.6 to explicitly mark "existential types", i.e., abstract boxed types
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that conform to a set of constraints. For source compatibility, these are not diagnosed by default
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except for existential types constrained to protocols with `Self` or associated type requirements
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(as this was introduced in the same version):
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```swift
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protocol Foo {
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associatedtype Bar
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func foo(_: Bar)
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}
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protocol Baz {}
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func pass(foo: Foo) {} // `any Foo` is required instead of `Foo`
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func pass(baz: Baz) {} // no warning or error by default for source compatibility
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```
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When enabled via `-enable-upcoming-feature ExistentialAny`, the upcoming language feature
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`ExistentialAny` will diagnose *all* existential types without `any`:
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```swift
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func pass(baz: Baz) {} // `any Baz` required instead of `Baz`
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```
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This will become the default in a future language mode.
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## Migration
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```sh
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-enable-upcoming-feature ExistentialAny:migrate
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```
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Enabling migration for `ExistentialAny` adds fix-its that prepend all existential types with `any`
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as required. No attempt is made to convert to generic (`some`) types.
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## See Also
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- [SE-0335: Introduce existential `any`](https://github.com/swiftlang/swift-evolution/blob/main/proposals/0335-existential-any.md)
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