Two new draft pattern matching JEPs

Brian Goetz brian.goetz at
Thu Feb 18 15:25:02 UTC 2021

On 2/18/2021 7:52 AM, Tagir Valeev wrote:
> Hello!
> Thank you!
> There's a sample in Nested Record and Array Patterns draft:
> static void printColorOfUpperLeftPoint(Object o) {
>      if (o instanceof Rectangle(ColoredPoint ul, ColoredPoint lr)){
>          if (ul instanceof ColoredPoint(Point p, Color c)) {
>              System.out.println(c);
>          }
>      }
> }
> It looks like here, the nested pattern "ul instanceof
> ColoredPoint(Point p, Color c)" is total. I thought that there's idea
> to prohibit total patterns with instanceof (at least total type test
> patterns are already prohibited). Please correct me if I'm wrong.

Slightly wrong :)

We prohibit total _type_ patterns in instanceof.  (Alternately, we could 
phrase it: we prohibit total patterns with empty remainder.) But a total 
record pattern is OK, because it has remainder { null }.

Recall the motivation: avoid confusion with `o instanceof Object`. Only 
the patterns where such a confusion could occur need to be restricted.

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