> On Dec 31, 2015, at 4:26 PM, Kevin Ballard <[email protected]> wrote:
>
> On Thu, Dec 31, 2015, at 01:40 PM, Michel Fortin wrote:
>> Le 30 déc. 2015 à 16:40, Kevin Ballard via swift-evolution
>> <[email protected]> a écrit :
>>> On Wed, Dec 30, 2015, at 01:33 PM, Joe Groff wrote:
>>>> Another possibility I've thought of is defining `defer { val }` to
>>>> guarantee that val remains alive until the defer fires on scope exit. That
>>>> might let us leave `defer` as the one "guarantee something happens exactly
>>>> at scope exit" language construct.
>>>
>>> Oh that's cute. I'd probably want to say `defer { _ = val }` though, to
>>> make it obvious that this is intentional.
>>
>> Or you could make it even more obvious what this is by giving that feature a
>> name. For instance:
>>
>> defer { _fixLifetime(val) }
>>
>> The good thing about this one is that it already works, because that's what
>> `withExtendedLifetime` does internally. Also, if you search a bit, you'll
>> end up here with a nice explanation of what that function does.
>> https://github.com/apple/swift/blob/8d9ef80304d7b36e13619ea50e6e76f3ec9221ba/stdlib/public/core/LifetimeManager.swift#L45
>>
>> So why not simply remove the underscore?
>
> Because it's not a very good API? Having some magic function called
> `fixLifetime()` that keeps values alive is a little weird.
> `withExtendedLifetime()` is also slightly weird, but it makes more sense than
> fixLifetime() does, since withExtendedLifetime() is the specific solution to
> the problem of "I need to ensure this value remains alive for this entire
> scope because reasons".
>
> I'd much rather just see the syntax `_ = val` be converted into
> `Builtin.fixLifetime(val)` because the only reason to write an expression
> like that is because you want to make sure the value is still alive at that
> point (that and because it's not unreasonable for people to assume that `_ =
> val` will keep the value alive, so it would be nice to make that assumption
> actually be correct).
I don't think this is obviously true. `val` could be a computed property you
just want to force the side effects for. (Computed properties with side effects
maybe aren't a great idea, but there are some in AppKit/UIKit.)
-Joe
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