[External] : Re: Make all switches exhaustive?

[Brian Goetz]

>
> This will not solve the problem of Maurizio for sub-patterns but i 
> like it.

I agree it doesn't *solve* the problem, but it helps somewhat.

> We don't have to later transform the warning to an error, keeping it 
> as a warning can be annoying enough to force people to change their 
> code (or ALT-ENTER + CTRL+1 ont it).

Yes, we can make this decision later.

>
>
>     Legacy switches are those whose operand type is one of the
>     "classic" types and all labels are constant labels or "default".
>
>     For a switch that is deliberately non-exhaustive, all the user has
>     to do to capture this (and shut up the compiler) is:
>
>         default: break;
>
>
> "default:" should be enough no ?

Yes, probably.

>
>
>     which is not very intrusive, and arguably makes the code more
>     readable anyway.  Users will see a speed bump when upgrading to
>     pattern switches (clippy will tell them "I see you're writing a
>     pattern switch, don't forget to end it with default:break") which
>     presumably they will quickly internalize.
>
>     (How's that for teaching an old dog new tricks?)
>
>
>
> I think we should tackle "default" not being at the end the same way.
>

I'd like that; pushing total patterns to the end is pretty helpful. We 
tried that once, and ran into trouble, though; there were cases we 
couldn't completely express with that IIRC.  With the latest formulation 
of `case null, default`, I think the trouble we ran into before goes 
away, but we might have new trouble doing so.
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