use strict;
use warnings;
use Data::Dumper;

my $obj = bless {}, "TST1";
my $str1 = Dumper $obj;

my $str2 = q($VAR1 = bless( {}, 'TST2' ););




package Bless::Safe;


use subs qw/bless/;

sub bless ($;$) {
    my ($obj,$class) = @_;
    die "Can't bless into non-existent Package $class"
      unless exists $main::{"${class}::"};
}


our $VAR1;

eval($str1) or $@ && die $@;                     # OK
eval($str2) or $@ && die $@;                     # FAILS

##</code><code>##

Can't bless into non-existent Package TST2 at d:/tmp/pm/override_bless.pl line 21.