Currently it’s not possible to have an unowned optional value. E.g:
class A {
unowned var parent : A? // ‘unowned’ may only be applied to class
and class-bound protocol types, not ‘A?'
deinit {
if let p = parent { print("Bye, mom!") }
print("deallocating")
}
}
Sometimes you want an unowned value, but it doesn’t actually need to be set.
In a specific case I was working on, we wanted to use a private embedded struct
to wrap some functionality away as a unit, but we need a reference back to the
enclosing instance. We could have a weak reference, but that comes with
additional overheads, and it’s unnecessary because that struct code will all
get inlined and the reference will just be a pointer back to ‘self’ (it would
be cool if the compiler could detect that and just not emit the variable at
all, but I don’t think it’ll do that). In any case, in order to initialise it
with the parent that reference needs to be an
optional/implicitly-unwrapped-optional (so that it can be initialised to nil
and then set after the parent calls super.init).
Given that weak optionals work, I’m tempted to think it’s a bug, but I’m asking
in case it was intentionally omitted.
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