> On Jul 25, 2017, at 3:26 PM, David Sweeris via swift-evolution > <[email protected]> wrote: > > > On Jul 25, 2017, at 12:38, Robert Bennett via swift-evolution > <[email protected] <mailto:[email protected]>> wrote: > >> Currently if you have the following enum: >> >> enum E<T> { >> case c(T) >> } >> >> then if T is Void, you have to write one of the following: >> >> let x: E<Void> = .c(Void()) >> let y: E<Void> = .c(()) >> >> Looks awkward, no? In this case you can omit `<Void>` after `E` because it >> can be inferred, but if writing a (non-generic) function taking an argument >> of type `E<Void>`, then the `<Void>` cannot be omitted, and you still have >> to write `.c(())` for the case name. >> >> I’m proposing that for enum cases with a single associated value of Void >> type, or of a generic type that is equal to Void in some instance, you may >> omit the parentheses altogether and merely write >> >> let x: E<Void> = .c >> >> The rationale is twofold: first, double parentheses just looks bad; second, >> there is only a single value of type Void, which means the associated value >> of `.c` is trivially inferable, and hence should be omissible. >> >> I am not proposing that a bare `E.c` imply a type of `E<Void>` — `E.c` >> should still be illegal in the absence of specification of the generic type >> — only that when the type is known to be `E<Void>`, `.c` can replace >> `.c(())`. >> >> Thoughts? > > My first response is +1 > > My second response is to ask just how much would it break things to expand > this and allow omitting the argument anywhere its type is known to be Void? > Maybe by implicitly providing a default value of `()` wherever there's a > `Void` argument? Like make `func foo(x: Void) {...}` implicitly become `func > foo(x: Void = ()) {...}`? I have a sneaking suspicion that this question's > already been asked, but I'm not sure.
I think default arguments for associated values have come up before. I would love to see that added someday. > > - Dave Sweeris > _______________________________________________ > swift-evolution mailing list > [email protected] > https://lists.swift.org/mailman/listinfo/swift-evolution
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