[swift-evolution] Warn about unused Optional.some(())
Charlie Monroe
charlie at charliemonroe.net
Tue Jan 31 00:16:58 CST 2017
> On Jan 31, 2017, at 1:03 AM, Matthew Johnson via swift-evolution <swift-evolution at swift.org> wrote:
>
>
>
> Sent from my iPad
>
>> On Jan 30, 2017, at 5:25 PM, Slava Pestov via swift-evolution <swift-evolution at swift.org> wrote:
>>
>>
>>> On Jan 30, 2017, at 2:58 PM, Daniel Duan via swift-evolution <swift-evolution at 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…
>
> +1
Isn't this how it was in Swift 2.x and the first versions of 3.0? I believe this was changed only recently - which I personally found as good news. In some cases you simply do not care about the error result since it has no impact if the call fails and typing "_ =" seemed like boilerplate...
If I recall correctly, this was discussed here on the list and changed to the current behavior.
>
>>
>>>
>>> What do y’all think?
>>>
>>> Daniel Duan
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>>
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