use warnings;
use strict;

package LoggingScalar {
  require Tie::Scalar;
  our @ISA = qw(Tie::StdScalar);
  
  sub FETCH { print "fetched: ".(${shift()} // '<undef>')."\n" }
}

tie my $x, 'LoggingScalar';
tie my $y, 'LoggingScalar';
tie my $z, 'LoggingScalar';
($x, $y, $z) = qw(x y z);

print "---\n";
my @a = ($x, $y . '!', $z);