[swift-evolution] [Proposal draft] Disallow Optionals in String Interpolation Segments

[Jordan Rose]

> On Oct 3, 2016, at 14:41, Kevin Ballard via swift-evolution <swift-evolution at swift.org> wrote:
> 
> On Mon, Oct 3, 2016, at 10:52 AM, Harlan Haskins via swift-evolution wrote:
>> Swift developers frequently use string interpolation as a convenient, concise syntax for interweaving variable values with strings. The interpolation machinery, however, has surprising behavior in one specific case: Optional<T>. If a user puts an optional value into a string interpolation segment, it will insert either "Optional("value")" or "nil" in the resulting string. Neither of these is particularly desirable, so we propose a warning and fix-it to surface solutions to these potential mistakes.
>> 
> 
> Is there any way we could instead allow Optionals but just print them the way we print ImplicitlyUnwrappedOptionals? That's almost always how I want my Optionals to work when interpolating. To be specific, this means for .some(x) we just print x, and for .none we print "nil".

We had this at one point, but we took it out because people would forget to test the nil case. I think `?? ""` or `?? nil` really is the best answer here.

Jordan

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