gistfile1.php

<?php

interface AccessorInterface
{
    function setClient(WebPay $client);
}

class WebPay
{
    protected $accessors = [];

    public function __construct()
    {
        // ...

        // register default accessors
        $this->registerAccessor('charges', new Charges());
        $this->registerAccessor('customers', new Customers());
        $this->registerAccessor('events', new Events());
        $this->registerAccessor('tokens', new Tokens());
        $this->registerAccessor('account', new Account());
    }

    public function registerAccessor($name, AccessorInterface $accessor)
    {
        $accessor->setClient($this);

        $this->accessors[$name] = $accessor;
    }
}