[swift-evolution] Proposal: Deprecate optionals in string interpolation

[David Waite]

> On May 19, 2016, at 11:01 PM, Krystof Vasa via swift-evolution <swift-evolution at swift.org> wrote:
> 
> With this proposal in place:
> 
> 1) The user would type print(myURL.path).
> 2) The compiler will immediately issue a warning about printing an optional - the user would hence learn about optionals *before* the code is run.
> 3) If he ran the code anyway, he'd still get Optional(/iphone/) anyway.
> 4) Xcode would offer a Fix-It, adding .debugDescription to the optional, getting Optional(/iphone/) on the anyway, yet again.

Four questions:
1. If I was printing a protocol type that Optional supports, such as Any, would I get a warning?
2. I believe debugDescription is discouraged from being called directly [from CustomDebugStringConvertible docs]. Perhaps String(reflecting: ) instead, although such debug description behavior could cause different results if you were expecting this fixit to apply to Any types.
3. How would I have the ability to opt into this behavior for my own types (such as Result or Future)?
4. How would I opt in/out of this behavior for my own StringInterpolationConvertible implementations?

-DW

> 
> I'm not saying *removing* the current behavior, but adding a warning for this - you'd get the same result ignoring the warning and applying the Fix-It, but you'd have control over this.
> 
>> On May 20, 2016, at 6:48 AM, Dan Appel via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> 
>> >google for swift print optional stackoverflow. I think that kind of speaks for itself.
>> 
>> I think this is actually an example of why the current behavior is a good thing. I did just google that and the top comment of the first result explains what an optional is. That is very good and encourages beginners to understand how optionals work under the hood. If you hide that from them, they will only be even more confused when they see just the string "nil" pop up when it previously was showing the correct value.
>> 
>> On Thu, May 19, 2016 at 9:36 PM Krystof Vasa via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> BTW - google for swift print optional stackoverflow. I think that kind of speaks for itself.
>> 
>> > On May 19, 2016, at 6:07 PM, Jeremy Pereira via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> >
>> > -1
>> >
>> > This seems to me like crippling string interpolation just because sometimes we make mistakes. 99% of the time, if I interpolate an optional, it’s because I want it that way. I don’t want to have to put up with a warning or write the same boilerplate 99% of the time just to flag up the 1% more easily. Sorry.
>> >
>> >> On 18 May 2016, at 19:50, Krystof Vasa via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> >>
>> >> The string interpolation is one of the strong sides of Swift, but also one of its weaknesses.
>> >>
>> >> It has happened to me more than once that I've used the interpolation with an optional by mistake and the result is then far from the expected result.
>> >>
>> >> This happened mostly before Swift 2.0's guard expression, but has happened since as well.
>> >>
>> >> The user will seldomly want to really get the output "Optional(something)", but is almost always expecting just "something". I believe this should be addressed by a warning to force the user to check the expression to prevent unwanted results. If you indeed want the output of an optional, it's almost always better to use the ?? operator and supply a null value placeholder, e.g. "\(myOptional ?? "<<none>>")", or use myOptional.debugDescription - which is a valid expression that will always return a non-optional value to force the current behavior.
>> >>
>> >> Krystof
>> >>
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>> Dan Appel
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