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

[Jeremy Pereira]

> On 3 Oct 2016, at 22:41, 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”.

On the other hand, when I interpolate an optional, I want it to be obvious that it is an Optional. If I didn’t want Optional(foo) in the string, I would unwrap it first. 

I also disagree with the proposal that the behaviour is surprising. What else would you expect? 

Having said that, I have no objection to the proposed warning.


> 
> -Kevin
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