On Tue, Oct 4, 2016, at 10:44 AM, Mark Lacey wrote: > >> On Oct 4, 2016, at 10:29 AM, Kevin Ballard via swift-evolution <swift- >> evolut...@swift.org> wrote: >> >> On Tue, Oct 4, 2016, at 10:28 AM, Nate Cook wrote: >>>> On Oct 3, 2016, at 5:49 PM, Kevin Ballard via swift-evolution <swift- >>>> evolut...@swift.org> wrote: >>>> >>>> On Mon, Oct 3, 2016, at 03:18 PM, Jordan Rose wrote: >>>>>> >>>>>> ... >>>>>> >>>>> 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. >>>> >>>> But you can't write that, unless you're dealing specifically with >>>> an Optional<String>. If you try you'll get an error: >>>> >>>> unnamed.swift:2:19: error: binary operator '??' cannot be applied >>>> to operands of type 'Int?' and 'String' >>>> print("x: \(x ?? "nil")") >>>> ~ ^ ~~~~~ >>>> unnamed.swift:2:19: note: overloads for '??' exist with these >>>> partially matching parameter lists: (T?, @autoclosure () throws -> >>>> T), (T?, @autoclosure () thro >>>> ws -> T?) >>>> print("x: \(x ?? "nil")") >>>> ^ >>>> This leads to writing code like "… >>>> \(x.map(String.init(describing:)) ?? "nil")" which is pretty gross. >>> >>> I think that if we're going to add this warning we should make it >>> possible to provide a string as an alternative. It seems like it >>> should be possible to build a ?? operator with a (T?, String) -> >>> _StringInterpolationSomething signature that works only in a string >>> interpolation context. >>> >>> There are some types that aren't trivially constructible, or don't >>> have clear alternatives for the nil case. Other times it might just >>> not make sense to build a new instance simply to turn it into a >>> string. If we're going to make people provide an alternative for >>> optionals in this otherwise simple-to-use construct, let's make it >>> simple to do so. >>> >>> This is undoubtedly a more complex approach that could be considered >>> separately, but I think it would be a valuable part of how >>> developers could transition their code. > > That’s definitely more complex, and seems like a completely orthogonal > feature request. > >>> >> I like this idea. This combined with the warning for naively >> interpolating an Optional would be a good solution, because now when >> I see the warning I can trivially solve it with `?? "nil”`. > > If you can suppress the warning with `as T?` (where T? is the type of > the thing being warned on), you wouldn’t need a form that specifically > printed “nil”, correct?
How many times do I need to repeat myself? I'm looking for a solution to the problem where printing Optionals sanely (e.g. no "Optional(…)" wrapper for .some values) is a PITA right now. Getting rid of the warning does not solve this problem. This is why I like Nate Cook's idea to enable `?? "nil"` in string interpolations, because it *does* solve my problem. And with this tool, now the warning on printing Optionals becomes useful because it tells me where to add `?? "nil"`. Getting rid of the warning without the ability to add `?? "nil"` is not helpful to me, because I don't want to print "Optional(…)". -Kevin Ballard
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