[Pitch] Non-Escapable Types and Lifetime Dependency

[tbkka (Tim Kientzle)]

@dmt

@tbkka It was initially proposed as @nonescaping modifier. However, it eventually became ~Escapable. Could you please expand on why?

Those are actually independent proposals. A few of us are focusing on the ~Escapable type property right now specifically because of the StorageView type, which requires something along these lines in order to provide strong safety guarantees.

The argument modifier is still interesting and I hope we'll have time to work on that sometime soon (if no-one else beats us to it ).

@dmt

Also, are non-escaping closures ~Escaping (and subject to lifetime modifiers)? Will it be possible to write this:

func f(_ g: borrowing () -> Void) -> copy(g) () -> Void { // not sure about `copy`
  g
}

Good question! That seems like a reasonable thing to me, but @Andrew_Trick knows the technical details better than I do. (It may not be something we'll be able to implement in the initial release of this feature.)

@dmt

PS:

• A copy(self) lifetime dependency with a borrowing or inout mutation-modifier

I believe it should be "borrowing or mutating"

Thank you for pointing that out! Fixed.