[swift-evolution] Auto Unwrapping Of Optionals

[Haravikk]

This is definitely something I’m hoping to see as well, alongside more intelligent handling of the is keyword, as currently Swift doesn’t handle the following either:

	if foo is SomeType { /* foo could be safely used as SomeType here, but currently is not */ }

Hopefully someone more familiar can weigh in, as it seems like something I expect to be on the way but perhaps has been delayed in case any further changes to the type system were required?

> On 29 Apr 2016, at 15:37, Tod Cunningham via swift-evolution <swift-evolution at swift.org> wrote:
> 
> I'm new to the swift evolution community, but I wanted to toss an idea out there to get some feedback on it. So here it goes...
> 
> Currently, if you assign a non-nil value to an optional and then want to access that optional later, in the same context, you need to manually unwrap the value.  This is usually done either by using "!" or by using something like "if let" or guard.
> 
> What would it be like if the compiler could auto unwrap, in cases where in knows the optional will have some value?  This would make the code "clean" and still be safe.
> 
> This concept of Auto Unwrapping of Optionals is similar to Implicitly Unwrapped Optionals, but is only applied when the compiler knows it is safe to do so.
> 
> Take the following example:
> 
> class Test {
>    var today: NSDate? = nil
>    func test() {
>        today = today ?? NSDate()
>        print("Today is \(today)")   // Would be printed as an optional
>        let timeInterval: NSTimeInterval = today!.timeIntervalSinceNow  // Requires ! or (if let) to unwrap
>        // ... do stuff with timeInterval ...
>    }
> }
> 
> With the above example, the compiler could known that today has a value after it's set in the test method.  So why couldn't the compiler auto unwrap it when accessed?  This would mean manual unwrapping would be unnecessary:
> 
> class Test {
>    var today: NSDate? = nil
>    func test() {
>        today = today ?? NSDate()
>        print("Today is \(today)")   // Would be printed as a value (not an optional)
>        let timeInterval: NSTimeInterval = today.timeIntervalSinceNow  // No ! required (auto unwrapped)
>        // ... do stuff with timeInterval ...
>    }
> }
> 
> If the value later gets set to an optional value, then it will no longer be auto unwrapable :
> 
> class Test {
>    var today: NSDate? = nil
> 
>    func optionalDay() -> NSDate? {
>        return NSDate()
>    }
> 
>    func test() {
>        today = today ?? NSDate()
>        print("Today is \(today)")   // Would be printed as a value (not an optional)
>        let timeInterval: NSTimeInterval = today.timeIntervalSinceNow    // No ! required (auto unwrapped)
>        let timeInterval2: NSTimeInterval = today!.timeIntervalSinceNow  // Explicit unwrapping would still be allowed
> 
>        // If today is assigned an optional value, we can no longer auto unwrap it
>        today = optionalDay()
>        print("Today is \(today)")   // Would be printed as an optional
>        let timeInterval3: NSTimeInterval = today!.timeIntervalSinceNow  // manual unwrapping would be required
>    }
> }
> 
> Note in the above example, explicit unwrapping would still be allow.  The variable is still an optional.  This allows for existing code to remain unchanged.
> 
> This change would encourage less use of forced unwrapping "!", generally require the developer to write less code, and would maintain code safety.  On the down side, it is performing some compiler “magic”.  It would be yet another thing to explain when trying to introduce people to swift and especially optionals.
> 
> What do you all think, would something like this be worth pursuing, what other pluses or minus would this introduce, has something like this already been discussed?
> 
> Thanks,
> Tod Cunningham
> 
> _______________________________________________
> swift-evolution mailing list
> swift-evolution at swift.org
> https://lists.swift.org/mailman/listinfo/swift-evolution

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