use strict;
use warnings;
use Data::Dump qw/pp dd/;

$|=1;


BEGIN {

    $\="\n";
    my $old =  $SIG{__WARN__};
    my $new_constant = sub() { 666 };
    *ALIEN::DOMAIN_PORT_NEW = sub() { 666 };

    $SIG{__WARN__} = sub {
        my ( $msg  ) = @_ ;

        if ($msg =~ /Constant subroutine DOMAIN_PORT redefined/ ) {
            $SIG{__WARN__} = $old;
            print "REDEFINED", pp caller;

            print ALIEN::DOMAIN_PORT();
            no warnings "redefine";
            *ALIEN::DOMAIN_PORT_OLD = *ALIEN::DOMAIN_PORT;
            *ALIEN::DOMAIN_PORT = *ALIEN::DOMAIN_PORT_NEW;
            print ALIEN::DOMAIN_PORT();
        }
    };

    *ALIEN::DOMAIN_PORT = sub () {"DUMMY"};

}




package ALIEN;

sub DOMAIN_PORT() {
    53
}




BEGIN {
    print "pre compile";
}

sub test {
    print "Inside test: ", DOMAIN_PORT;
}


test();

##</code><code>##

REDEFINED("main", "d:/tmp/pm/patch_constant.pl", 39)
DUMMY
666
pre compile
Inside test: 53