Anonymous Classes

**Anonymous classes, introduced in PHP 7, are a unique and useful feature that allows developers to define and instantiate a class in a single expression without explicitly naming the class. **They're particularly helpful when a full class declaration seems excessive for simple use cases or when you only need the class for a short period within your code.

Key Characteristics:

• No Name: As the name suggests, anonymous classes don't have a name.
• On-the-Fly: They are defined and can be instantiated in a single expression.
• Scoped: Anonymous classes have access to the outer scope, much like closures in PHP.
• One-off Use: They're typically used for one-time tasks where a formal class declaration isn't necessary.

Creating an Anonymous Class

Anonymous classes are simple to create. All you have to do is define the class with the new keyword and assign the instance to a variable like so:

$greeting = new class {
  public function sayHello() {
    return 'Hello, World!';
  }
};
 
echo $greeting->sayHello();  // Outputs: Hello, World!

In the above example, we've defined an anonymous class with a method sayHello(). We've instantiated the class and called its method, all without ever giving the class a formal name.

What's supported?

Anonymous classes in PHP are quite versatile and support many features that standard named classes do. Here's what you can do with anonymous classes:

1. Inheritance: An anonymous class can extend another class, thereby inheriting its methods and properties.

$child = new class extends ParentClass {
  // methods and properties of ParentClass are available here
};

2. Interfaces: An anonymous class can implement one or more interfaces.

$worker = new class implements WorkableInterface {
  public function work() {
    // Implementation of the work method from the WorkableInterface
  }
};

3. Traits: Anonymous classes can use traits, just as named classes can.

$traitUser = new class {
  use SomeTrait;
  // rest of the class
};

4. Public, Protected, and Private: They can have public, protected, and private methods and properties, just like any other class.
5. Constructor: Anonymous classes can have their own constructors.

$obj = new class("Hello") {
  public function __construct(private $greeting) {
  }
 
  public function greet() {
    return $this->greeting;
  }
};
echo $obj->greet();  // Outputs: Hello

6. Magic Methods: They can use magic methods, like __get(), __set(), __invoke(), etc.
7. Nesting: Anonymous classes can be nested within other classes or even within other anonymous classes.

Given their support for these features, anonymous classes can be as complex as needed.

When to use them?

Anonymous classes can be quite handy in specific scenarios.

• When you need a class for a short-lived task or single use and don't want to litter your codebase with one-off class definitions.
• They're particularly useful for creating mock objects in unit tests. Instead of defining a whole new mock class or using a mock library, you can simply use an anonymous class tailored to your immediate needs.
• When you're in scenarios where class requirements might change dynamically based on conditions, anonymous classes can be employed to handle such variations.

While anonymous classes can be very handy, they should be used judiciously. Overusing them could make the code harder to understand and maintain, especially for larger and more complex structures. They're best suited for lightweight tasks or when dealing with libraries/frameworks that require objects with specific interfaces or traits for brief durations.

Key Takeaways

• Anonymous classes are a feature in PHP that allows the definition and instantiation of a class without a name in a single expression.