Parametrized protocol types #40714
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Parametrized protocol types #40714
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And ban them in other inheritance clauses.
Previously we would resolve the constraint type of an `any` using TypeResolverContext::GenericRequirement, but this does not allow us to distinguish between parametrized protocol types in generic requirements (which are supported) from parametrized protocol types inside an `any`, like `any Sequence<Int>`, which is not supported for now.
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@DougGregor I'm curious if this Just Works with #40993... |
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@swift-ci Please smoke test |
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This allows you to write constructs like
Sequence<Int>in generic requirement-like contexts:whereclausesWith the first three, the new syntax is just sugar. With opaque result types though, it gives you the ability to express something that could not previously be expressed.
The protocol must declare a primary associated type (for now, using the
@_primaryAssociatedTypeattribute; this part isn't final). Assuming that the primary associated type ofSequenceisElement, the desugaring is thatT : Sequence<Int>is equivalent toT : Sequence where T.Element == Int.Note that currently, neither
Sequencenor any other standard library type actually use this new attribute. You can only use it with your own protocols for now.This is all gated by the
-enable-parametrized-protocol-typesflag, since this is an unofficial feature. I'll send out an evolution pitch soon.