[adamwk]

The way to write performant Swift is classless so without ARC, but classes have been necessary for many areas. Recently, Swift’s been leveraging a lot of ownership features similar to Rust to make it possible to do more without classes, and I’d guess Apple teams would be using those

[sunnybeetroot]

What areas are classes necessary assuming you’re talking about pure Swift and not iOS?

[adamwk]

Where copying is expensive (most Swift collections are backed by classes for COW semantics). Where location stability is necessary (where you need a mutex). Resource allocation. Those are the primary examples that noncopyable types are meant to address.