स्टैटिक प्रॉपर्टी और विधियाँ

<?php
class AppConfig {
    private static array $settings = [];

    public static function set(string $key, mixed $val): void {
        self::$settings[$key] = $val;
    }

    public static function get(string $key, mixed $default = null): mixed {
        return self::$settings[$key] ?? $default;
    }
}

AppConfig::set('debug', true);
echo AppConfig::get('debug') ? 'debug on' : 'debug off';

<?php
class MathHelper {
    public static function clamp(float $v, float $min, float $max): float {
        return max($min, min($max, $v));
    }

    public static function lerp(float $a, float $b, float $t): float {
        return $a + ($b - $a) * $t;
    }
}

echo MathHelper::clamp(150, 0, 100); // 100
echo MathHelper::lerp(0, 100, 0.5);  // 50

<?php
class Database {
    private static ?Database $instance = null;

    private function __construct() {
        echo 'Connected to DB';
    }

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

$db1 = Database::getInstance();  // 'Connected to DB'
$db2 = Database::getInstance();  // no output — same instance
echo ($db1 === $db2) ? 'same' : 'different'; // same

<?php
class EventEmitter {
    private static int $instanceCount = 0;

    public function __construct() {
        self::$instanceCount++;
    }

    public static function count(): int {
        return self::$instanceCount;
    }
}

new EventEmitter();
new EventEmitter();
new EventEmitter();
echo EventEmitter::count();  // 3

<?php
class ParentClass {
    public static function create(): static {
        return new static();  // resolves to calling subclass
    }

    public function getClass(): string {
        return static::class;  // late static binding
    }
}

class ChildClass extends ParentClass {}

$obj = ChildClass::create();
echo $obj->getClass();  // ChildClass

<?php
class Response {
    private function __construct(
        private int   $status,
        private mixed $body
    ) {}

    public static function ok(mixed $data): self {
        return new self(200, $data);
    }

    public static function notFound(): self {
        return new self(404, ['error' => 'Not Found']);
    }

    public function toJson(): string {
        return json_encode(['status' => $this->status, 'body' => $this->body]);
    }
}

echo Response::ok(['users' => []])->toJson();

<?php
// Static: no object needed, but harder to test/mock
class Validator {
    public static function isEmail(string $s): bool {
        return (bool) filter_var($s, FILTER_VALIDATE_EMAIL);
    }
}

// Instance: injectable dependency, testable
class ValidatorService {
    public function isEmail(string $s): bool {
        return (bool) filter_var($s, FILTER_VALIDATE_EMAIL);
    }
}
// Prefer instance classes in larger applications