use feature qw( say );
use experimental qw( refaliasing declared_refs );

my $y = 1;     # Make `$y` have the same value as `1`.
say $y;        # 1
$y = 2;        # Make `$y` have the same value as `2`. 
say $y;        # 2

my \$x = \1;   # Make `$x` an alias of `1`.
say $x;        # 1
$x = 2;        # Modification of a read-only value attempted
say $x;