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Since these different forms of documentation have a similar purpose, and there's already some infrastructure for educational notes, unify all of the diagnostics-related documentation in a single place. We might consider unifying these ideas in the compiler as well, but that's for another day.
25 lines
891 B
Markdown
25 lines
891 B
Markdown
# `ExistentialAny`
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This diagnostic group includes errors and warnings pertaining to the `any` type
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syntax proposed in [SE-0335].
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`any` syntax draws a line between constraint types and existential or boxed
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types.
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For example, `any Collection` is a boxed type abstracting over a value of a
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dynamic type that conforms to the protocol `Collection`, whereas the
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`Collection` part is the conformance constraint imposed on the type of the
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underlying value *as well as* a constraint type.
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The distinction between a conformance constraint and a constraint type can be
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clearly seen in classic generic syntax: `<T: Collection>`.
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Constraint types exist to express conformances and have no meaning in relation
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to values.
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```swift
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func sillyFunction(collection: Collection) { // error
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// ...
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}
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```
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[SE-0335]: https://github.com/swiftlang/swift-evolution/blob/main/proposals/0335-existential-any.md
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