PolyMorphismExample.php

<?php

class Engine
{
    private $pk;

    public function __construct(int $pk)
    {
        $this->pk = $pk;
    }
}

interface ElectricVehicleInterface {
    public function isPluginHybrid(): bool;
}

interface CombustionVehicleInterface {}

interface VehicleInterface
{
    public function getEngine(): \Engine;

    public function setEngine(\Engine $engine);
}

abstract class AbstractAuto implements Vehicle
{
    protected $engine;

    public function getEngine(): \Engine
    {
        return $this->engine;
    }

    abstract function setEngine(\Engine $engine): void;
}

class Fiat extends AbstractAuto implements ElectricVehicleInterface
{
    private $isHybrid = false;
    
    public function __construct(bool $isHybrid)
    {
        $this->isHybrid;
    }

    public function getEngine(): \Engine
    {
        return $this->engine;
    }

    public function isPluginHybrid(): bool
    {
        return $this->isHybrid;
    }

    public function setEngine(\Engine $engine)
    {
        $this->engine = $engine;
    }
}

class FordMustang extends AbstractAuto implements CombustionVehicleInterface
{
    public function setEngine(\Engine $engine)
    {
        $this->engine = "$engine x 2";
    }
}

class Garage
{
    private $vehicles;

    public function __construct()
    {
        $this->vehicles = array();
    }

    public function addVehicle(\VehicleInterface $auto)
    {
        if ($auto instanceof \ElectricVehicleInterface) {
            // Do discount.
            if ($auto->isHybrid()) {
                // Do less discount.
            }
        }

        $this->vehicles[] = $auto;
    }
}

$fiat = new Fiat();
$fiat->setEngine(new Engine(10));

$mustang = new FordMustang();
$mustang->setEngine(new Engine(400));

$garage = new Garage();
$garage->addVehicle($fiat);
$garage->addVehicle($mustang);