perl inheritance and directory structure -

i'm trying learn inheritance in perl.

this directory structure:
perldir
perldir\child.pl
perldir\mylib
perldir\mylib\parent.pm

parent.pm

package parent;  sub new {      $class = shift;     $self = { _first => shift, _last => shift };     bless $self, $class; }  sub getfirstname {     ($self) = @_;     return $self->{ _first }; }  1; 

child.pl

package child;  use parent 'mylib::parent';  sub new {      $class = shift;     $self = parent->new( shift, shift );     bless $self, $class; }  $obj = new child('jack', 'sparrow'); print $obj->{_first},' ',$obj->{_last}; print "\n",$obj->getfirstname();  #error 

the error thrown on last line is: can't locate object method "getfirstname" via package "achild" @ child.pl line 13;

the program works if 1 of following:
1. have both files under directory mylib.
2. replace

use parent 'mylib::parent' 

with

use mylib::parent; @isa = ('parent'); 

is possible program work using 'use parent' , child class in different directory?

==========================
updated question based on choroba's answer.

ok changed classes reflect following:

parent.pm

package mylib::parent;  sub new {      $class = shift;     $self = { _first => shift, _last => shift };     bless $self, $class; }  sub getfirstname {     ($self) = @_;     return $self->{ _first }; }  1; 

child.pl

package child;  use parent 'mylib::parent';  sub new {      $class = shift;     $self = mylib::parent->new( shift, shift );     bless $self, $class; }  $obj = new child('jack', 'sparrow'); print $obj->{_first},' ',$obj->{_last}; print "\n",$obj->getfirstname(); 

the above works fine. consider want child class in same directory parent.pm.

perldir\mylib\childtwo.pl

package childtwo;   #or package mylib::childtwo;  use parent 'mylib::parent'; #or use parent 'parent';  sub new {      $class = shift;     $self = mylib::parent->new( shift, shift ); #or parent->new(shift, shift);     bless $self, $class; }  $obj = new childtwo('jack', 'sparrow'); #or new mylib::childtwo('jack','sparrow'); print $obj->{_first},' ',$obj->{_last}; print "\n",$obj->getfirstname();  1; 

the above not work. can childtwo.pl work along child.pl without using 'use lib'?

you have make mind: either parent package's name parent, in child.pl:

use parent 'parent'; 

and tell perl search it:

perl -imylib child.pl 

or use lib

use findbin; use lib "$findbin::bin/mylib"; 

or, package's name mylib::parent, have fix package declaration:

package mylib::parent; 

and call correct constructor:

my $self = mylib::parent->new( shift, shift );