[swift-evolution] [Proposal] Remove force unwrapping in function signature.

Dennis Lysenko dennis.s.lysenko at gmail.com
Mon Jun 27 15:35:06 CDT 2016 

+1. This is sort of how Kotlin does it. In Kotlin, IUOs are strictly a
carryover from Java. They show up in method signatures from
non-nullable-annotated Java, but you can't define a new method that takes
e.g. an Int!.

The limited scope of this proposal is ideal in my opinion since we see
areas where IUOs are clearly useful (ViewControllers for instance) but
defining new functions that take implicitly unwrapped optionals makes no
sense. If you need to pass a IUO at the call site, you can define the
function taking a non-optional value and pass the IUO to that. There is no
use case I can think of for having it in method/function signatures.

RE: language inconsistencies, there is no such issue in practice in Kotlin
where there is also inconsistency in the same vein. I see it simply as a
compromise that achieves the goal of keeping a useful feature but
discouraging its overuse by forbidding its use in places where its use
could confuse and snowball down the line into teaching developers worse
code quality.

On Mon, Jun 27, 2016 at 12:04 PM Charlie Monroe via swift-evolution <
swift-evolution at swift.org> wrote:

> Ok, I see - though I find myself using occasionally IUOs in Swift as well
> - e.g. when you can't use the default values because they depend on self,
> etc.
>
> Eliminating it just from method signatures IMHO brings an incosistency
> into the language. Why would you eliminate it only from method signatures -
> this proposal mentioned importing ObjC API in the beginning - why not then
> mark those properties all as optional as well? IUOs are scheduled to be
> removed completely once the language reaches a point where it can handle
> most scenarios otherwise...
>
> Try to imagine some APIs brought to Swift with default being nullable:
>
> /// Imported from
> public class NSOrderedSet : NSObject, NSCopying, NSMutableCopying,
> NSSecureCoding, NSFastEnumeration {
>
>
>     public var count: Int { get }
>     public func objectAtIndex(idx: Int) -> AnyObject?
>     public func indexOfObject(object: AnyObject?) -> Int
>     public init()
>     public init(objects: UnsafePointer<AnyObject?>, count cnt: Int)
>     public init?(coder aDecoder: NSCoder?)
> }
>
> This doesn't make much sense - mostly objectAtIndex(_:).
>
> On Jun 27, 2016, at 8:35 PM, Saagar Jha <saagarjha28 at gmail.com> wrote:
>
> I think you’re mistaking the scope of the proposal. It’s simply removing
> IUOs in *function signatures*, not throughout the language.
>
> On Mon, Jun 27, 2016 at 11:31 AM Charlie Monroe via swift-evolution <
> swift-evolution at swift.org> wrote:
>
>> There are many useful cases for IUO in Swift - mostly when you have
>> variables that cannot be calculated at the point of calling super.init(),
>> but are guaranteed to be filled during initialization - i.e. during the
>> lifetime of the object, the value is nonnil, but may be nil for a short
>> period of time.
>>
>> Or @IBOutlets. Making all @IBOutlets optionals would make the code either
>> riddled with ! or shadowed locally re-declared instance members.
>>
>>
>> > On Jun 27, 2016, at 8:12 PM, Jean-Daniel Dupas <mailing at xenonium.com>
>> wrote:
>> >
>> > Maybe we can prohibit it in Swift function declaration, and allow it
>> only when importing native code.
>> >
>> > As David, I don’t see any compelling reason to allow such construct in
>> Swift.
>> >
>> >> Le 27 juin 2016 à 10:39, Charlie Monroe via swift-evolution <
>> swift-evolution at swift.org> a écrit :
>> >>
>> >> When you import ObjC code that has no nullability annotation, IUO make
>> sense since:
>> >>
>> >> - they can be checked against nil
>> >> - typically, most values in APIs are nonnull (looking at Foundation,
>> for example, which is why Apple has the NS_ASSUME_NONNULL_BEGIN to mark
>> entire regions as nonnull, yet there is no NS_ASSUME_NULL_BEGIN)
>> >>
>> >> Importing them as optionals would make it really hard to work with the
>> code - whenever you get a value, it's an optional, even in cases where it
>> makes no sense and adding ! to unwrap the optional is not a great solution.
>> And the other solution is to use guards everywhere.
>> >>
>> >> IMHO the IUO is a nice (temporary) solution for using un-annotated
>> code until it is. But the "pressure" should be applied on the ObjC code.
>> >>
>> >>> On Jun 27, 2016, at 10:03 AM, David Rönnqvist <
>> david.ronnqvist at gmail.com> wrote:
>> >>>
>> >>> I don’t know about the chances of getting approved, but I think this
>> is something worth discussing.
>> >>>
>> >>> It might just be my ignorance, but I can’t think of a good reason why
>> a function argument would be force unwrapped. Either it’s non-null and the
>> caller is expected to unwrap it or it’s nullable and the method is expected
>> to handle the nil value. So I’m positive to that part of the proposal.
>> >>>
>> >>> As to what we should do with the generated interfaces of Objective-C
>> code that hasn’t been annotated with nullability, I think that needs input
>> from more people to find the preferred solution.
>> >>>
>> >>> Once that’s been discussed some more, I’d be willing to write up a
>> formal proposal if you don’t feel like it (assuming the discussion leads
>> somewhere).
>> >>>
>> >>> - David
>> >>>
>> >>>
>> >>>> On 27 Jun 2016, at 06:28, Charlie Monroe via swift-evolution <
>> swift-evolution at swift.org> wrote:
>> >>>>
>> >>>> See https://github.com/apple/swift-evolution/blob/master/process.md
>> - you would need to make an official proposal and submit it as pull
>> request. But given the reaction here, it's unlikely to get approved.
>> >>>>
>> >>>> Also, the ObjC code without nullability is getting fairly rare - all
>> Apple's frameworks are with nullability information (as far as I've
>> checked) in macOS 10.12, iOS 10. Third party libraries should be updated to
>> use nullability (and most libraries that are maintained already do).
>> >>>>
>> >>>>
>> >>>>> On Jun 25, 2016, at 5:13 PM, Spromicky via swift-evolution <
>> swift-evolution at swift.org> wrote:
>> >>>>>
>> >>>>> So, its proposal is dead, or what we must to do to force it to
>> swift-evolution repo on GitHub?
>> >>>>>
>> >>>>>> Hello, everyone!
>> >>>>>>
>> >>>>>> I wanna propose to you to remove force unwrapping in fuction
>> signature for swift code. That no sense in clear swift code. If we wanna
>> use some optional value as function param, that is not optional, we must
>> unwrap it before function call.
>> >>>>>> People who new in swift look at how they old Obj-C code (without
>> nullability modifiers) translate in to swift:
>> >>>>>>
>> >>>>>> Obj-C:
>> >>>>>> - (void)foo:(NSInteger)bar {
>> >>>>>> //...
>> >>>>>> }
>> >>>>>>
>> >>>>>> Swift transaliton:
>> >>>>>> func foo(bar: Int!) {
>> >>>>>> //...
>> >>>>>> }
>> >>>>>>
>> >>>>>> And think that force unwrapping in signature is good practice. And
>> start write functions in clear swift code like this:
>> >>>>>>
>> >>>>>> func newFoo(bar: Int!) {
>> >>>>>> //...
>> >>>>>> }
>> >>>>>>
>> >>>>>> and use it like this:
>> >>>>>>
>> >>>>>> let bar: Int? = 1
>> >>>>>> newFoo(bar)
>> >>>>>>
>> >>>>>> And it really work, and they does not think that this can crash in
>> case if `bar` will be `nil`.
>> >>>>>> But in clear swift we wanna work with parametrs in function that
>> clearly or optional, or not.
>> >>>>>>
>> >>>>>> func newFoo(bar: Int) {
>> >>>>>> //...
>> >>>>>> }
>> >>>>>>
>> >>>>>> or
>> >>>>>>
>> >>>>>> func newFoo(bar: Int?) {
>> >>>>>> //...
>> >>>>>> }
>> >>>>>>
>> >>>>>> When we write a new function we know what we need in this case and
>> use optional params or not.
>> >>>>>>
>> >>>>>> So my proposal is remove force unwrapping(`!`) from function
>> signatures, cause it have no sense, and that confuse new users.
>> >>>>>>
>> >>>>>>
>> >>>>>>
>> >>>>> _______________________________________________
>> >>>>> swift-evolution mailing list
>> >>>>> swift-evolution at swift.org
>> >>>>> https://lists.swift.org/mailman/listinfo/swift-evolution
>> >>>>
>> >>>> _______________________________________________
>> >>>> swift-evolution mailing list
>> >>>> swift-evolution at swift.org
>> >>>> https://lists.swift.org/mailman/listinfo/swift-evolution
>> >>>
>> >>
>> >> _______________________________________________
>> >> swift-evolution mailing list
>> >> swift-evolution at swift.org
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>> >
>>
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>>
> --
> -Saagar Jha
>
>
> _______________________________________________
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