Not sure if this requires a proposal. The code change is pretty trivial:
https://github.com/apple/swift/pull/7154
<https://github.com/apple/swift/pull/7154> .
> On Jan 30, 2017, at 3:25 PM, Slava Pestov <spes...@apple.com> wrote:
>
>>
>> On Jan 30, 2017, at 2:58 PM, Daniel Duan via swift-evolution
>> <swift-evolution@swift.org> 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.
>
> IMHO, using ‘try?’ to ignore an error result, instead of just turning it into
> an optional, is an anti-pattern, and forcing users to write ‘_ = try? foo()’
> might not be so bad…
>
>>
>> What do y’all think?
>>
>> Daniel Duan
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