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

[Jeremy Pereira]

> On 3 Oct 2016, at 11:14, Adrian Zubarev via swift-evolution <swift-evolution at swift.org> wrote:
> 
> I know that there is this note in Commonly Rejected Changes:
> 
> 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?
> 
> 

I absolutely cannot see why 

    default: break

doesn’t already do this for you. It’s not a useless no-op, it signifies to the compiler that you really do want to ignore the other cases and it’s not a mistake.

I think there is a case for allowing default: break to be at the top of the switch but other than that, I like the fact that not having a an explicitly exhaustive switch generates an error.


> 
> 
> -- 
> Adrian Zubarev
> Sent with Airmail
> 
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