1.2. Builder

1.2.1. Purpose

Builder is an interface that build parts of a complex object.

Sometimes, if the builder has a better knowledge of what it builds, thisinterface could be an abstract class with default methods (aka adapter).

If you have a complex inheritance tree for objects, it is logical tohave a complex inheritance tree for builders too.

Note: Builders have often a fluent interface, see the mock builder ofPHPUnit for example.

1.2.2. Examples

• PHPUnit: Mock Builder

1.2.3. UML Diagram

1.2.4. Code

You can also find this code on GitHub

Director.php

<?php
 
namespace DesignPatterns\Creational\Builder;
 
use DesignPatterns\Creational\Builder\Parts\Vehicle;
 
/**
 * Director is part of the builder pattern. It knows the interface of the builder
 * and builds a complex object with the help of the builder
 *
 * You can also inject many builders instead of one to build more complex objects
 */
class Director
{
    public function build(BuilderInterface $builder): Vehicle
    {
        $builder->createVehicle();
        $builder->addDoors();
        $builder->addEngine();
        $builder->addWheel();
 
        return $builder->getVehicle();
    }
}

BuilderInterface.php

<?php
 
namespace DesignPatterns\Creational\Builder;
 
use DesignPatterns\Creational\Builder\Parts\Vehicle;
 
interface BuilderInterface
{
    public function createVehicle();
 
    public function addWheel();
 
    public function addEngine();
 
    public function addDoors();
 
    public function getVehicle(): Vehicle;
}

TruckBuilder.php

<?php
 
namespace DesignPatterns\Creational\Builder;
 
use DesignPatterns\Creational\Builder\Parts\Vehicle;
 
class TruckBuilder implements BuilderInterface
{
    /**
     * @var Parts\Truck
     */
    private $truck;
 
    public function addDoors()
    {
        $this->truck->setPart('rightDoor', new Parts\Door());
        $this->truck->setPart('leftDoor', new Parts\Door());
    }
 
    public function addEngine()
    {
        $this->truck->setPart('truckEngine', new Parts\Engine());
    }
 
    public function addWheel()
    {
        $this->truck->setPart('wheel1', new Parts\Wheel());
        $this->truck->setPart('wheel2', new Parts\Wheel());
        $this->truck->setPart('wheel3', new Parts\Wheel());
        $this->truck->setPart('wheel4', new Parts\Wheel());
        $this->truck->setPart('wheel5', new Parts\Wheel());
        $this->truck->setPart('wheel6', new Parts\Wheel());
    }
 
    public function createVehicle()
    {
        $this->truck = new Parts\Truck();
    }
 
    public function getVehicle(): Vehicle
    {
        return $this->truck;
    }
}

CarBuilder.php

<?php
 
namespace DesignPatterns\Creational\Builder;
 
use DesignPatterns\Creational\Builder\Parts\Vehicle;
 
class CarBuilder implements BuilderInterface
{
    /**
     * @var Parts\Car
     */
    private $car;
 
    public function addDoors()
    {
        $this->car->setPart('rightDoor', new Parts\Door());
        $this->car->setPart('leftDoor', new Parts\Door());
        $this->car->setPart('trunkLid', new Parts\Door());
    }
 
    public function addEngine()
    {
        $this->car->setPart('engine', new Parts\Engine());
    }
 
    public function addWheel()
    {
        $this->car->setPart('wheelLF', new Parts\Wheel());
        $this->car->setPart('wheelRF', new Parts\Wheel());
        $this->car->setPart('wheelLR', new Parts\Wheel());
        $this->car->setPart('wheelRR', new Parts\Wheel());
    }
 
    public function createVehicle()
    {
        $this->car = new Parts\Car();
    }
 
    public function getVehicle(): Vehicle
    {
        return $this->car;
    }
}

Parts/Vehicle.php

<?php
 
namespace DesignPatterns\Creational\Builder\Parts;
 
abstract class Vehicle
{
    /**
     * @var object[]
     */
    private $data = [];
 
    /**
     * @param string $key
     * @param object $value
     */
    public function setPart($key, $value)
    {
        $this->data[$key] = $value;
    }
}

Parts/Truck.php

<?php
 
namespace DesignPatterns\Creational\Builder\Parts;
 
class Truck extends Vehicle
{
}

Parts/Car.php

<?php
 
namespace DesignPatterns\Creational\Builder\Parts;
 
class Car extends Vehicle
{
}

Parts/Engine.php

<?php
 
namespace DesignPatterns\Creational\Builder\Parts;
 
class Engine
{
}

Parts/Wheel.php

<?php
 
namespace DesignPatterns\Creational\Builder\Parts;
 
class Wheel
{
}

Parts/Door.php

<?php
 
namespace DesignPatterns\Creational\Builder\Parts;
 
class Door
{
}

1.2.5. Test

Tests/DirectorTest.php

<?php
 
namespace DesignPatterns\Creational\Builder\Tests;
 
use DesignPatterns\Creational\Builder\Parts\Car;
use DesignPatterns\Creational\Builder\Parts\Truck;
use DesignPatterns\Creational\Builder\TruckBuilder;
use DesignPatterns\Creational\Builder\CarBuilder;
use DesignPatterns\Creational\Builder\Director;
use PHPUnit\Framework\TestCase;
 
class DirectorTest extends TestCase
{
    public function testCanBuildTruck()
    {
        $truckBuilder = new TruckBuilder();
        $newVehicle = (new Director())->build($truckBuilder);
 
        $this->assertInstanceOf(Truck::class, $newVehicle);
    }
 
    public function testCanBuildCar()
    {
        $carBuilder = new CarBuilder();
        $newVehicle = (new Director())->build($carBuilder);
 
        $this->assertInstanceOf(Car::class, $newVehicle);
    }
}