in reply to keys on scalar warnings and lack thereof

perl -e '$_[0]={1,1,2,2};keys %$_[0]'     # no
perl -e '$_[0]={1,1,2,2};print ref $_[0]' # wtf
HASH

[download]

Precedence rules ...

$ perl -E'$_[0]={1,1,2,2};say keys %{$_[0]}'   # ttf°
21
$

[download]

Cheers Rolf
(addicted to the Perl Programming Language :)
see Wikisyntax for the Monastery

°) s/what/this/

In Section Seekers of Perl Wisdom