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$ perl -E'%h=(a=>1,b=>1,c=>1); while (my ($k) = each(%h)) { say $k; }'
c
...
c
a
b

$ perl -E'my @a = (4,5); say 0+@a; delete $a[10]; say 0+@a;'
2
2

$ perl -E'my %h; delete $h{x}; say "ok";'
ok

$ perl -E'my %h = (x=>1); delete $h{x}; delete $h{x}; say "ok";'
ok