Warn about unused Optional.some(())


(James Froggatt) #1

Would this affect optional chaining? ( a?.voidReturningFunc() also evaluates to ()? )

------------ Begin Message ------------
Group: gmane.comp.lang.swift.evolution
MsgID: <1FA68175-BC14-4E61-AECE-A80B79D55065@apple.com>

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…

···

On Jan 30, 2017, at 2:58 PM, Daniel Duan via swift-evolution <swift-evolution@swift.org> wrote:

What do y’all think?

Daniel Duan
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------------- End Message -------------

From James


(Daniel Duan) #2

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@swift.org> wrote:

Would this affect optional chaining? ( a?.voidReturningFunc() also evaluates to ()? )

------------ Begin Message ------------
Group: gmane.comp.lang.swift.evolution
MsgID: <1FA68175-BC14-4E61-AECE-A80B79D55065@apple.com>

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
_______________________________________________
swift-evolution mailing list
swift-evolution@swift.org
https://lists.swift.org/mailman/listinfo/swift-evolution

_______________________________________________
swift-evolution mailing list
swift-evolution@swift.org
https://lists.swift.org/mailman/listinfo/swift-evolution

------------- End Message -------------

From James
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swift-evolution mailing list
swift-evolution@swift.org
https://lists.swift.org/mailman/listinfo/swift-evolution