Constructor Method

Classes can have something called magic methods. Magic methods in PHP are special predefined methods that have specific names starting with two underscores (__). These methods are triggered automatically in response to certain actions. In other words, they're "magical" because you don't explicitly call them; PHP does it for you when a specific condition is met.

Think of a magic method like an automatic door at a grocery store. When you approach the door (or meet a condition), it opens automatically (or the method is called) without you needing to do anything.

The construct method

For example, one of the most commonly used magic methods is the __construct() method. This method is automatically called when you create a new object from a class. It's often used to set initial values for object properties.

Here's an example:

class Dog {
  public $name;
 
  // This is the magic constructor method
  public function __construct($dogName) {
    $this->name = $dogName;
  }
}
 
$rex = new Dog('Rex'); // The __construct method is automatically called here
echo $rex->name; // Outputs 'Rex'

In this example, when we instantiate the Dog object ($rex), PHP automatically calls the __construct() method and passes 'Rex' as the argument. This sets the $name property of the new object.

Constructor Promotion

Constructor property promotion is a feature added in PHP 8.0 that provides a shorthand syntax to define class properties and a constructor in a single declaration.

Before this feature, if you wanted to define a class with properties, and those properties were to be set via the __constructor(), you would have to do something like this:

class Dog {
  public $name;
  public $age;
 
  public function __construct($name, $age) {
    $this->name = $name;
    $this->age = $age;
  }
}
 
$rex = new Dog('Rex', 5);

Here, we had to manually declare the properties $name and $age, then we had to define a constructor function that takes $name and $age as arguments, and finally, we had to assign those arguments to the corresponding properties using $this->.

With constructor property promotion, this boilerplate code can be greatly reduced. We can define properties directly in the constructor like this:

class Dog {
  public function __construct(public $name, public $age) {
    // nothing else needed here
  }
}
 
$rex = new Dog('Rex', 5);

In this case, PHP automatically creates the $name and $age properties for us and assigns the passed values to them. This makes our class definition shorter and cleaner.

So, to sum up, constructor property promotion is a shorthand way of defining class properties and a constructor at the same time, making your code more compact and readable. It's one of the great new features added in PHP 8.0.

Key takeaways

• Magic methods in PHP are special methods that start with two underscores (__) and are triggered automatically when certain conditions are met.
• The __construct() method is a magic method that's automatically invoked when an object is created from a class.
• It's commonly used to initialize object properties or to perform actions needed for object setup.
• The __construct() method can take parameters, allowing you to pass values when creating a new object.
• Constructor property promotion is a feature added in PHP 8.0 that simplifies the creation of classes.
• It allows you to define class properties directly in the constructor, reducing boilerplate code.