Under our proposal you can return to the old semantics of printing nil with an explicit optional cast - one which we will offer to insert for you.
Otherwise if you actually intend for a default value that value would have type Int, not String. Under the current regime if you want to print something custom the for nil the way you've got it now you're going to have to go through the reflecting initializer anyway so I don't see a problem here. ~Robert Widmann 2016/10/03 19:25、Charlie Monroe via swift-evolution <swift-evolution@swift.org> のメッセージ: > I've already suggested this quite some time back and was told that this > doesn't need to go through evolution. It's filed here: > https://bugs.swift.org/browse/SR-1882 > > Unfortunately, I haven't had time to look into it myself and I'm unlikely to > have the time anytime soon... > >> On Oct 3, 2016, at 7:52 PM, Harlan Haskins via swift-evolution >> <swift-evolution@swift.org> wrote: >> >> Hey all, >> >> Julio Carrettoni, Robert Widmann, and I have been working on a proposal to >> mitigate something that's burned us all since Swift 1. We'd love some >> feedback! >> >> It's available here: >> https://gist.github.com/harlanhaskins/63b7343e7fe4e5f4c6cfbe9413a98fdd >> >> I've posted the current draft below. >> >> Thanks, >> Harlan Haskins >> >> Disallow Optionals in String Interpolation Segments >> Proposal: SE-NNNN >> Authors: Harlan Haskins, Julio Carrettoni, Robert Widmann >> Review Manager: TBD >> Status: Awaiting revie >> Introduction >> >> 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. >> >> Swift-evolution thread: Discussion thread topic for that proposal >> >> Motivation >> >> The Swift Programming Language defines string interpolation segments as "a >> way to construct a new String value from a mix of constants, variables, >> literals, and expressions". There is one type that runs counter to this >> definition: Optional. The .none case in particular is used to indicate the >> absence of a value. Moreover, its inclusion in interpolation segments leads >> to the dreaded "nil" in output that is often fed to UI elements. Even >> barring that, interpolating a non-nil optional value yields >> "Optional("value")", a result that is not useful even in logged output. >> >> Given that the Optional type is never fit for display to the end user, and >> can often be a surprising find in the console, we propose that requesting an >> Optional's debug description be an explicit act. This proposal now requires >> a warning when using an expression of Optional type within a string >> interpolation segment. >> >> Proposed solution >> >> The user will be warned after attempting to use an expression with type >> Optional<T> in a string interpolation segment. They will then be offered a >> fixit suggesting they explicitly request the debugDescription of the >> Optional value instead. >> >> Detailed design >> >> Semantic analysis currently does not do much but guarantee the >> well-formedness of expressions in interpolation segments. These are then fed >> directly to String.init(stringInterpolationSegment:) and are run through the >> runtime reflection system to generate a description. Semantic analysis will >> be tweaked to inspect the result of solving an interpolation segment for an >> Optional and will offer a fixit in that case. >> >> Impact on existing code >> >> As this is a warning, code written before this proposal will continue to >> compile and run with the same semantics as before. Authors of code that >> makes use of this unsafe pattern will be offered a migration path to the >> safer, more explicit form. >> >> Alternatives considered >> >> A fixit that suggests a default value be inserted would be entirely >> appropriate (following the style of the fixit introduced in SE-0140). >> >> Forbidding this pattern by hard error would make this proposal a breaking >> change that is out of scope for this stage of Swift's development. >> >> A fixit that introduces a force-unwrapping would technically work as well, >> however it would be fixing a dangerous operation with yet another dangerous >> operation. >> >> >> >> Sent from my iPad >> _______________________________________________ >> swift-evolution mailing list >> swift-evolution@swift.org >> https://lists.swift.org/mailman/listinfo/swift-evolution > > _______________________________________________ > swift-evolution mailing list > swift-evolution@swift.org > https://lists.swift.org/mailman/listinfo/swift-evolution
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