Interesting. I certainly agree with
a simple ($key) = %$hash_ref would have done the trick better
for clarity, terseness and, more important, lack of side effects. Unless a hash is huge:
>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; s
+ay time - $^T; say $k"
10
176
4034296
with equally bad effects on memory. Looks like keys in void context is harmless (performance-wise), but assignment of a hash to single-element list is not
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