c:\@Work\Perl>perl  -MO=Deparse,-p  -le
"use warnings;
 use strict;
 ;;
 print qq{Perl ver.: Strawberry $]};
 ;;
 package XX {
   use constant to_1 =>  42;
   use constant to_2 => 999;
   }
 ;;
 package YY {
   use parent -norequire, 'XX';
   use constant to_2 => 137;
   }
 ;;
 my $y = bless {} => 'YY';
 ;;
 print $y->to_1;
 print $y->to_2;
 ;;
 print YY->to_1;
 print YY->to_2;
 ;;
 print XX::to_1;
 print XX::to_2;
 print YY::to_2;
 ;;
 print YY::to_1;
"
Name "YY::to_1" used only once: possible typo at -e line 1.
BEGIN { $/ = "\n"; $\ = "\n"; }
sub YY::to_2 () { 137 }
sub XX::to_2 () { 999 }
sub XX::to_1 () { 42 }
use warnings;
use strict 'refs';
print("Perl ver.: Strawberry $]");
package XX;
sub BEGIN {
    require constant;
    do {
        'constant'->import('to_1', 42)
    };
}
use constant ('to_2', 999);
package main;
{;};
package YY;
sub BEGIN {
    require parent;
    do {
        'parent'->import((-'norequire'), 'XX')
    };
}
use constant ('to_2', 137);
package main;
{;};
(my $y = bless({}, 'YY'));
print($y->to_1);
print($y->to_2);
print('YY'->to_1);
print('YY'->to_2);
print(42);
print(999);
print(137);
print(YY::to_1 $_);
-e syntax OK