In Swift, String? is an alias to Optional<String>. Optional is an enumeration wi... | Hacker News

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		manmal on March 29, 2025 \| parent \| context \| favorite \| on: You Need Subtyping In Swift, String? is an alias to Optional<String>. Optional is an enumeration with two cases: some, and none, where the former has the non-nil value attached. I‘m not sure how that ties in with subtyping though.

ackfoobar on April 8, 2025 [–]

> how that ties in with subtyping

In Swift it does not. But in Kotlin, `String?` is not an enum (sum type), but instead means `String | null`, a union type.

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