New candidate JEP: 455: Primitive types in Patterns, instanceof, and switch (Preview)

[Attila Kelemen]

>
>
> As it turns out, your first example is nonsensical:
>
>
> ```
> switch (p) {
>     case Pair!(Pair?(A a, B b), Pair?(C c, D d)): ...
> }
> ```
>
>
> Here, the nested pattern `Pair?(A a, B b)` makes no sense, because it is a
> record pattern, and a record pattern *cannot* match null (because it needs
> a non-null receiver on which to invoke the accessors and/or
> deconstructor.)  So even in a world with emotional type patterns, this
> pattern would be rejected by the compiler as illegal.
>

Yeah, I don't know how I missed that, because I actually considered the
same thing for `case Pair?(Pair? a, Pair? b)` and realized that it makes no
sense ...

But then I assume if we had `Pair` declared as `record Pair<A, B>(A? a, B?
b) {}`, then I could use this to not match a `Pair` instance with null
fields:

```
switch (p) {
    case Pair!(String! a, String! b): ...
}
```

And writing `String` would be inferred to be `String?` in this case.
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