use v6-alpha;
use Test;
=pod
You can specify 'is copy' on an arg and modify it inside a function,
but this bug prevents it when the argument is optional *and* has a
default value.
(Note that "is copy = 0" is fine but "= 0 is copy" is not.)
=cut
plan 1;
sub boom ($arg is copy = 0) { $arg++ }
lives_ok { boom(42) }, "can modify a copy";