It's not directly related to property behaviors. It was a bug that only worked
with ImplicitlyUnwrappedOptional properties; we patched the type checker bug
that led to it being allowed and didn't even notice until someone brought it up
(SR-5172 <https://bugs.swift.org/browse/SR-5172>).
It would be possible to introduce this as an actual language feature even
without the full property behaviors model, but we wouldn't want to just spell
it 'lazy'. Maybe 'lazy_resettable' or something. And even though I say this,
it's probably unlikely that such a proposal would get through swift-evolution
in the Swift 5 timeframe.
Meanwhile, it's always possible to implement it by hand, though I can see how
that'd be annoying if you were relying on this and previously got it with a
single '!'.
class LazyResettableTest {
private func fooInitial() -> String { return "initial value" }
private var fooStorage: String?
var foo: String! {
get {
if fooStorage == nil { fooStorage = fooInitial() }
return fooStorage
}
set {
fooStorage = newValue
}
}
}
Jordan
> On Oct 19, 2017, at 19:59, David Sweeris via swift-users
> <[email protected]> wrote:
>
> I don't know. IIRC (big if), though, there was talk of adding support for
> "property behaviors"(?). Resetting lazy vars probably would've been one of
> them, and if so, it probably got pulled so that we wouldn't risk breaking
> source compatibility later by adding a consistent syntax for other behaviors.
> I think. I wish I could remember who'd brought up the idea... they'd probably
> know straight away if that's what happened.
>
> - Dave Sweeris
>
>> On Oct 19, 2017, at 5:40 PM, Rick Mann via swift-users
>> <[email protected]> wrote:
>>
>> Googling for the answer, it seemed some versions of Swift supported setting
>> a lazy var property to nil, such that the next time it's accessed, the
>> initializer would be run again.
>>
>> But I just tried this in a playground in Swift 4 and it doesn't work.
>>
>> It sure seems to me like it should work. What's the reasoning for the
>> current behavior?
>>
>> --
>> Rick Mann
>> [email protected]
>>
>>
>> _______________________________________________
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>> https://lists.swift.org/mailman/listinfo/swift-users
>
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