In PHP, When to Use Static Methods?

Static methods in PHP belong to a class, rather than an instance of that class. They can be called directly on the class itself, without needing to create an object instance from that class. Here are a few scenarios when it may be beneficial to use static methods in PHP:

1. Utility Functions: When you have a method that performs a task without affecting object state or needing any data from an object instance, it can be made static. For instance, mathematical operations, string formatting functions, or file system operations could be implemented as static methods in a utility class.

   class Util {
       public static function formatPhoneNumber($number) {
           // Format the phone number here and return it
       }
   }
   
   echo Util::formatPhoneNumber('1234567890');
   

2. Singleton Pattern: If you’re implementing the Singleton pattern (a design pattern that restricts a class from instantiating more than one object), you’ll use a static method to provide global access to the single instance.

   class Singleton {
       private static $instance;
   
       private function __construct() { /* ... */ }
   
       public static function getInstance() {
           if (null === static::$instance) {
               static::$instance = new static();
           }
   
           return static::$instance;
       }
   }
   
   $singleton = Singleton::getInstance();
   

3. Factory Pattern: The Factory pattern (a design pattern to create objects) often employs a static method as a central location to create and return new instances of a class.

   class CarFactory {
       public static function create($make, $model) {
           return new Car($make, $model);
       }
   }
   
   $car = CarFactory::create('Ford', 'Mustang');
   

While static methods can be useful, it’s also important to use them judiciously. Overuse of static methods can lead to code that is difficult to test and maintain, due to tight coupling between classes and lack of ability to substitute dependencies (a feature provided by object-oriented programming). This is something to be mindful of when choosing to use static methods.