Lazy Loading with Closures

listing1.php

<?php
// client code
$customer = $customerRepository->find($id);
$orders = $customer->getOrders();

listing2.php

<?php
class Customer
{
    public function getOrders()
    {
        $ordersData = $this->db->query(/* select orders... */);
        $orders = array();)
        foreach($ordersdata as $orderdata) {
            $orders[] = new Order($orderdata);
        }
        return $orders;
    }
}

listing3.php

<?php
class Customer
{
    public function getOrders()
    {
        return $this->orders;
    }
}

class CustomerRepository
{
    public function find($id)
    {
        $customerdata = $this->db->query(/* select customer ...*/);
        $customer = new Customer($customerdata);

        $ordersdata = $this->db->query(/* select orders ... */);
        foreach($ordersdata as $orderdata){
            $customer->addOrder(new Order($orderdata));
        }
    }
}

listing4.php

<?php
class Customer
{
    public function setOrdersReference(Closure $ordersReference)
    {
        $this->ordersReference = $ordersReference;
    }

    public function getOrders()
    {
        if(!isset($this->orders)) {
            $reference = $this->ordersReference;
            $this->orders = $reference();
        }
        return $this->orders;
    }
}

class CustomerRepository
{
    public function find($id)
    {
        $db = $this->db;
        $customerdata = $db->query(/* select customer ...*/);
        $customer = new Customer($customerdata);

        $ordersReference = function($customer) use($id, $db) {
            $ordersdata = $db->query(/* select orders ... */);
            $orders = array();
            foreach($ordersdata as $orderdata) {
                $orders[] = new Order($orderdata);
            }
            return $orders;
        };
        $customer->setOrderReference($ordersReference);
        return $customer;
    }
}

Aren't you missing a return $orders; in listing4.php?

@md2perpe Thanks, fixed.