__START_OF_COMMON_LIB_FILE__
package Class1;
sub new {
    return bless({}, 'Class1');
}

sub method_1 {
    print "I'm method 1!\n";
}

package Class2;
sub new {
    return bless({}, 'Class2');
}

sub method_2 {
    print "I'm method 2!\n";
}

1;
__END_OF_COMMON_LIB_FILE__

##</code><code>##

use lib 'C:\tmp';
use CommonLib;

my $class1_obj = Class1->new;
my $class2_obj = Class2->new;

$class1_obj->method_1;
$class2_obj->method_2;
##</code><code>##

D:\tmp>tmp.pl
I'm method 1!
I'm method 2!

D:\tmp>
##</code><code>##

use CommonLib;

my $class1_obj = Class1->new;
my $class2_obj = Class2->new;

$class1_obj->method_2;
$class2_obj->method_1;
##</code><code>##

D:\tmp>tmp.pl
Can't locate object method "method_2" via package "Class1" at D:\tmp\tmp.pl line 10.

D:\tmp>
##</code><code>##

package Class1;
package Class2;

sub foo {
}