When several patterns are total ?

[Brian Goetz]

,
> i've hinted that there is an issue with intersection type and totality, but we did not follow up.
> 
> Here is the issue
> var value = flag? "foo": 42;
> switch(value) {
>  case String s -> ...
>  case Integer i -> ...
>  case Serializable s ->
>  case Comparable<?> c ->  
> }
> 
> given that the type of value is an intersection type Serializable & Comparable<?> & ...
> the last two cases are total with respect to the type of value. which does not go well with the current semantics that can only have one total case.

Let’s separate the issues here.  The type involved is an infinite type, which I think we can agree is a distraction.  But lets assume the type of value were Serializable&Comparable (S&C for short.)  

Because S&C <: S, the `case S` in your example is already total, so the `case C` should be a dead case and yield a compilation error.  According to the rule we have, `case S` is total on any U <: S, so it is total on S&C, so the current model covers this, and the `case C` is identified as dead by the compiler.  Which makes sense because there’s no value it can match.

I’m not seeing the problem?