PHP 関数の設計パターンとベスト プラクティス

abstract class ShapeFactory
{
    abstract public function createShape(string $shapeType): Shape;
}

class CircleFactory extends ShapeFactory
{
    public function createShape(string $shapeType): Shape
    {
        if ($shapeType === 'circle') {
            return new Circle();
        }
        throw new InvalidArgumentException();
    }
}

$circleFactory = new CircleFactory();
$circle = $circleFactory->createShape('circle');

class Database
{
    private static $instance;

    private function __construct() {}

    public static function getInstance(): Database
    {
        if (self::$instance === null) {
            self::$instance = new Database();
        }
        return self::$instance;
    }
}

// 此处只能获取 Database 的一个实例
$db1 = Database::getInstance();
$db2 = Database::getInstance();
if ($db1 === $db2) {
    echo '同一实例';
}

function calculateArea(Shape $shape)

function calculateArea(Shape $shape)
{
    switch ($shape->getType()) {
        case 'circle':
            return pi() * $shape->getRadius() ** 2;
        case 'rectangle':
            return $shape->getWidth() * $shape->getHeight();
    }
}

function calculateArea(Shape $shape): float

function calculateArea(Shape $shape, float $scale = 1.0): float

class CalculateAreaTest extends PHPUnit\Framework\TestCase
{
    public function testCircleArea()
    {
        $shape = new Circle(3);
        $this->assertEquals(28.27, calculateArea($shape), '', 0.01);
    }
}