No, that won't fly. You need 
$seen{$_}++ for @list;
my @doubles = grep $seen{$_} == 2, @list;

[download]

Makeshifts last the longest.

In reply to Re^3: Perl Idioms Explained - keys %{{map{$_=>1}@list}} by Aristotle
in thread Perl Idioms Explained - keys %{{map{$_=>1}@list}} by broquaint

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