[swift-evolution] [Pitch] Can we make `default` on switches optional?

[Xiaodi Wu]

-1 from me as well. This suggestion falls into the same category as those
about making `else` optional after `guard`, which is repeatedly rejected.
Since code is read more often than written, explicit handling of the
default case never hurts and can increase clarity. Not having to write
`default: break` offers no help in writing correct code and IMO can't
justify new syntax or the changing of a well-known control statement.

On Mon, Oct 3, 2016 at 11:39 AM, Robert Widmann via swift-evolution <
swift-evolution at swift.org> wrote:

> -1 in general.  I want smarter exhaustiveness analysis, but I don’t want
> to be able to ignore cases that “can’t happen” (so say we, writer of bugs)
> when they’re clearly in the domain of possible values that can be fed to a
> switch-case.  Exhaustiveness guarantees wellformedness of a program that
> does happen to go wrong, and makes it much easier to verify the correctness
> of the flow of control of the containing block because all points from the
> switch must be covered.  We also don’t have the type-level tools to
> convince the checker to allow you to remove unreachable cases.  If it’s
> really a problem that you are writing default cases everywhere, just
> bailout in a fatal error with a nice description.  It never hurts.
>
> ~Robert Widmann
>
> On Oct 3, 2016, at 6:14 AM, Adrian Zubarev via swift-evolution <
> swift-evolution at swift.org> wrote:
>
> I know that there is this note in Commonly Rejected Changes
> <https://github.com/apple/swift-evolution/blob/master/commonly_proposed.md>
> :
>
> Remove support for default: in switch and just use case _:: default is
> widely used, case _ is too magical, and default is widely precedented in
> many C family languages.
>
> I really like to use the switch instead of if case for pattern matching,
> just because it’s neat block design. I do not want to remove default from
> switches because it’s a must have and powerful feature.
>
> I’d like to know why switches must be exhaustive.
>
> switch someValue {
>
> case …:
>     // Do something
>
> case …:
>     // Do something else
>
> default:
>     () // useless nop; do nothing when no pattern matched
> }
>
> // VS:
>
> if case … {
>
> } else if case … {
>
> } else if case … {
>
> } // No need for `else`
>
> Can’t we make default optional, or at least on non-enum values?
>
>
>
> --
> Adrian Zubarev
> Sent with Airmail
>
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