>perl -E "$h{$_} = $_ for 0 .. 5_000_000; say time - $^T; keys %h; say time - $^T; $k = scalar each %h; say time - $^T; say $k"
10
10
10
852569

>perl -E "$h{$_} = $_ for 0 .. 5_000_000; say time - $^T; ($k) = %h; say time - $^T; say $k"
10
176
4034296