Amendment to the history of the bug after I had a look at the bug reports
again: SR-1895 <https://bugs.swift.org/browse/SR-1895> explicitly asked that
let s: String? = "hi"
s.map {print($0)}
should not produce any warnings while it did so during beta 1.
– Alex
> On 31 Jan 2017, at 09:07, Alex Hoppen via swift-evolution
> <[email protected]> wrote:
>
> This was a deliberate change between Swift 3 beta 1 and beta 2 after a friend
> of mine pointed the following inconsistency out to me:
>
> struct Foo {
> func bar() {}
> }
> let foo: Foo? = Foo()
> foo?.bar() // Does not create a warning
> true ? foo?.bar() : foo?.bar() // expression of type '()?' is unused
>
> After some offline discussion at WWDC with the Swift team we decided to move
> to a consistent model where ()?, ()??, … is always discardable since we
> didn't want to take the convenience of foo?.bar() away (something that
> regularly occurs with weak variables, e.g. captures in closures).
>
> So much for the history of this feature.
>
> – Alex
>
>
>> On 30 Jan 2017, at 22:58, Daniel Duan via swift-evolution
>> <[email protected]> wrote:
>>
>> Hi all,
>>
>> Right now, expressions that evaluates to Optional<()>,
>> Optional<Optional<()>>… gets special treatment when it’s unused. For example:
>>
>> func f(s: String) {}
>> let s: String = “”
>> s.map(f) // no warning here, even tho the resulting type is `Optional<()>`
>> and unused.
>>
>> func g() throws {}
>> try? g() // no warnings here neither.
>>
>> This is convenient, but encourages composing map/filter/reduce, etc with
>> side-effect-ful functions, which we have found a few cases of in our
>> production code recently. Granted, these cases could’ve been caught with
>> more careful code reviews. But we wouldn’t have missed them if this
>> “feature” didn’t exist.
>>
>> I think we should remove the special treatment so that code in the example
>> above would generate a warning about `()?` being unused. Users can silence
>> it manually by assigning the result to `_`.
>>
>> OTOH, this would undermine the convenience of `try?` when the throwing
>> function don’t return anything.
>>
>> What do y’all think?
>>
>> Daniel Duan
>> _______________________________________________
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>
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