[swift-evolution] Warn about unused Optional.some(())
Daniel Duan
daniel at duan.org
Mon Jan 30 19:37:27 CST 2017
As implemented, no. Whether it should be affected is another topic...
> On Jan 30, 2017, at 5:17 PM, James Froggatt via swift-evolution <swift-evolution at swift.org> wrote:
>
> Would this affect optional chaining? ( a?.voidReturningFunc() also evaluates to ()? )
>
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>
>> 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…
>
>>
>> What do y’all think?
>>
>> Daniel Duan
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