> On 15 Aug 2016, at 21:27, Xiaodi Wu <xiaodi...@gmail.com> wrote: > > On Mon, Aug 15, 2016 at 1:57 PM, Haravikk via swift-evolution > <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote: > >> On 15 Aug 2016, at 13:44, Tim Vermeulen <tvermeu...@me.com >> <mailto:tvermeu...@me.com>> wrote: >> >>>> On 15 Aug 2016, at 08:02, Justin Jia via >>>> swift-evolution<swift-evolution@swift.org >>>> <mailto:swift-evolution@swift.org>(mailto:swift-evolution@swift.org >>>> <mailto:swift-evolution@swift.org>)>wrote: >>>> Hi! >>>> >>>> I don’t know if this has came up before. I tried to search though the >>>> mailing list but didn’t find any related threads. >>>> >>>> This is purely a syntactic thing (which I know it’s the lowest priority >>>> for Swift 4), but I think it’s an important one. >>>> >>>> Let’s say we have a struct with a function: >>>> >>>> ``` >>>> struct Foo { >>>> func bar(x: Int) >>>> } >>>> ``` >>>> >>>> We can use optionals: >>>> >>>> ``` >>>> let foo: Foo? = nil >>>> let x = 1 >>>> foo!.bar(x: x) // Able to compile, but will cause runtime error >>>> foo?.bar(x: x) // Able to compile, and won't cause runtime error >>>> ``` >>>> >>>> However: >>>> >>>> ``` >>>> let foo = Foo() >>>> let x: Int? = nil >>>> foo.bar(x: x!) // Able to compile, but will cause runtime error >>>> foo.bar(x: x?) // Won't compile >>>> ``` >>>> >>>> I propose that we should allow `foo.bar(x: x?)`, which should be >>>> equivalent to: >>>> >>>> ``` >>>> if let x = x { >>>> foo.bar(x: x) >>>> } >>>> ``` >>>> >>>> What do you think? >>> I like the intent behind this, but personally I think it's not clear >>> enough. For me, putting the statement in a conditional as you've shown is >>> the better solution, as it's a lot clearer exactly what's going on. Putting >>> a question mark on a variable makes it look like something specific to that >>> variable, rather than preventing the entire statement from executing. >> >> I get where you’re coming from, but how would people react if optional >> chaining wasn’t in the language yet and someone proposed it now? I know it’s >> not strictly the same thing, but it’s still a single question mark that >> prevents the whole statement from being executed. I think it would be met >> with a lot of resistance from people saying that being more explicit with >> `if let` is the way to go. > > True, but with optional chaining the position of the question mark makes it a > lot more clear where it stops, whereas in this proposal the question mark > seems a bit less intuitive since it's within the parenthesis yet affecting > the statement outside of it. > >>> There may be some alternatives though, for example, what about a shorthand >>> for the conditional like so: >>> >>> if let x? { foo.bar(x: x) } >>> if x? { foo.bar(x: x) } // even shorter? >> >> The alternatives you’ve come up with would only work if foo.bar doesn’t >> return anything. If it does return something, and you want to assign it to a >> variable, you have to declare the variable beforehand and it just becomes >> ugly. It’s then probably a better idea to use map/flatmap: > > Hmm, what about something involving the where keyword? Something like: > > let value = foo.bar(x: x) where x? > > Some people have queried the ability to use where in assignments before, as > another way to have a statement be nil if a condition isn't met, but in this > case the condition is that x is unwrapped (thus valid for the call). This > basically lets you use it like a "retroactive" conditional, it'd be nice to > get the same x? behaviour on for loops anyway (letting you unwrap values that > way, and maybe test them too). > > `let value = (x == nil) ? nil : foo.bar(x: x)` isn't so bad, is it?
In my opinion, it is. And you’d even need to write `foo.bar(x: x!)`, right? > You could even write a custom operator to sugar it. > > > _______________________________________________ > swift-evolution mailing list > swift-evolution@swift.org <mailto:swift-evolution@swift.org> > https://lists.swift.org/mailman/listinfo/swift-evolution > <https://lists.swift.org/mailman/listinfo/swift-evolution> > >
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