Classes and objects

Objects bundle data and behavior. PHP supports classes, interfaces, traits, enums (PHP 8.1+), and readonly properties (PHP 8.2+).

Basic class

class User {
    public function __construct(
        public string $name,
        public string $email,
    ) {}

    public function label(): string {
        return $this->name;
    }
}

$u = new User('Ada', 'ada@example.com');

Constructor property promotion

PHP 8 shorthand declares and assigns properties in the constructor parameter list—common in DTOs and value objects.

$this

Inside instance methods, $this refers to the current object. Static methods use self:: or static::.

Important interview questions and answers

1. Q: Class vs object?
   A: Class is the blueprint; object is an instance created with new.
2. Q: When use readonly properties?
   A: Immutable value objects initialized once in the constructor—PHP 8.2+.

Self-check

1. What keyword creates an instance?
2. What does constructor promotion save you from writing?

Tip: Constructor property promotion (PHP 8) keeps DTOs short—pair with readonly properties when values must not change.