use strict;
use warnings;

package Foo;

sub new { bless {salary => 100} }

my $private_method = sub {
    my $self   = shift;
    my $factor = shift || 2;
    $self->{salary} *= $factor;
};

sub get_salary {
    my $self = shift;
    $self->$private_method(10);
    return $self->{salary};
}

package main;

my $foo = Foo->new;
printf "salary is %s\n", $foo->get_salary;