use strict;
use warnings;

my @x = qw ( a b c d e ff ggg hhhh iiii );
my %y;

# Tata!!! Here comes the requested line of code:

noLoop(); sub noLoop { $y{pop(@x)} = 1; noLoop() if (scalar(@x)); }  # btw.: using global vars in subs is usually bad style ;-)

print keys(%y), "\n";
exit 0;