... without introducing a new variable ...

The following variation doesn't introduce a new variable because  $_ already exists! (I believe the following is also Stupid Hash Trick #58.)

>perl -wMstrict -le
"for ({ qw(a 1  b 2  c 3) }) {
   while (my ($k, $v) = each %$_) {
     print qq{$k => $v};
     }
   }
"
c => 3
a => 1
b => 2
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