> On Jan 12, 2018, at 12:53 PM, BJ Homer via swift-evolution > <swift-evolution@swift.org> wrote: > > I agree that this behavior is annoying. However, wouldn’t it be > source-breaking to change this now?
Source compatibility means that we can't change the behavior of Swift 3 / Swift 4 source. This would be a semantic change when building Swift 5 source (or later). There is no technical reason we couldn't make this change. It does need to meet a very high bar, because we are trying to avoid making significant semantic breaks. My personal sense is that it meets that bar because double-optionals can be very confusing for novices and very annoying for everyone else. I think most use sites probably do want the optional-collapsing behavior. 'try?' is already "sugar" syntax and should aim to be as convenient as possible for the majority of use cases. Much like the collapsing done by optional chaining, I think you can come up with examples where somebody would want the non-collapsing behavior, but it doesn't seem unreasonable to say that they just shouldn't use the sugar. John. > > -BJ > >> On Jan 12, 2018, at 10:25 AM, Russ Bishop via swift-evolution >> <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote: >> >> Greetings swift-evolution! >> >> There is currently a disconnect between optional chaining and try? when it >> comes to optional flattening: >> >> >> struct SomeType { >> func nonThrow() -> SomeType? { return self } >> func doThrow() throws -> SomeType? { return self } >> func nonOptional() throws -> SomeType { return self } >> } >> >> let w = SomeType().nonThrow()?.nonThrow()?.nonThrow()?.nonThrow() >> // w has type SomeType? >> >> let x = try? >> SomeType().nonOptional().nonOptional().nonOptional().nonOptional() >> // x has type SomeType? >> >> let y = try! SomeType().doThrow()?.doThrow()?.doThrow()?.doThrow() >> // y has type SomeType? >> >> let z = try? SomeType().doThrow()?.doThrow()?.doThrow()?.doThrow() >> // z has type SomeType?? >> >> >> We get a double-optional only when combining try? and optional-chaining. >> That is inconvenient and it would be natural to have the compiler do the >> flattening here. >> >> >> If anyone is interested in working on the proposal or implementation please >> let me know. It would make a nice self-contained task if you're looking to >> start contributing. >> >> >> Russ Bishop >> Simulator >> >> >> _______________________________________________ >> swift-evolution mailing list >> swift-evolution@swift.org <mailto: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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