[Accepted] SE-0390: Noncopyable structs and enums

Joe_Groff · May 25, 2023, 11:46pm

Thanks Steve! I have amended the proposal to follow the Language Steering Group's recommendations:

github.com/apple/swift-evolution

Updates to SE-0390 to correspond to current implementation

apple:main ← jckarter:se-0390-may-2023-checkpoint

opened 11:59PM - 15 May 23 UTC

jckarter

+177 -14

- Doing flow sensitive escape analysis to allow for locals to be consumed before… they get escapingly captured is too hard and probably not really worth it. Just say that they always behave as escaped if they ever are escaped. - Local `let` bindings to closure literals are considered nonescaping if the `let` doesn't escape. This falls out of the existing analysis built into the mandatory SIL passes. - Deinit `self` is immutable for now, while we debate the proper way to handle mutation and consumption while controlling the potential for accidental recursion.

I have also subset out a couple of aspects of the original proposal to correspond to what we've been able to implement so far:

The proposal had specified that local variables escaped by closures become non-consumable after the point they get escaped by a closure, but we weren't able to implement this flow sensitive analysis, and the added expressivity seemed minor, so I've subset the proposal to have it so that escaped local variables are never consumable. We can potentially implement the originally proposed behavior later.
We are leaving self within deinits immutable for now, while we discuss the best way to allow for deinits to perform mutations and consumptions while mitigating the potential for accidental infinite recursion by implicit deinits elsewhere.