#!/usr/bin/perl -w
use strict;
package Foo;

{
    # private
    my $set_a = sub {
        my $self = shift;
        $self->{a} = shift;
    };

    # public
    sub a {
        my $self = shift;
        return $self->{a};
    }

    # public
    sub new {
        my $self = bless {},shift;
        $self->$set_a('abcdef');
        return $self;
    }
}

package main;

my $foo = Foo->new;
print $foo->a();