Elizabeth Mattijsen via RT wrote: >A Pair in which the value is a container, is mutable.
Not really. The *container* is mutable. The Pair can't be changed to refer to any other container, as far as I can see: > my $a; my $b = :a($a); my $c = :a($a); $b.value = 3; $b.perl, $c.perl (:a(3) :a(3)) I've mutated something there, but it's not one of the pairs to the exclusion of the other. It's the thing they share, the value container. These pairs should therefore show the same identity under .WHICH. I'd expect the .WHICH string to be something like "Pair|Str|a|Scalar|47608575457088". -zefram
