Example of Dependency Injection

injection2.php

<?php
class ClassConvertMoneyWithInjection
{
    /** @var IConversor */
    public $service;
    public function setService(IConversor $srv) {
        $this->service=$srv;
    }
    public function example($money) {
        echo "$money is converted in ".$this->service->conversor($money)."<br>";
    }
}
interface IConversor {
    function conversor($value);
}

class ServiceEuroToDollar implements IConversor {
    function conversor($value)
    {
        return $value*1.15;
    }
}

class ServiceDollarToEuro implements IConversor {
    function conversor($value)
    {
        return $value/1.15;
    }
}