Classes, Objects & Constructor Property Promotion

In Plain English

PHP features a complete, modern Object-Oriented Programming (OOP) model. Learn class definitions, instantiation ($obj = new ClassName()), methods ($this->method()), destructors (__destruct), and PHP 8 constructor property promotion for zero-boilerplate field assignments.

The Mental Model

"A class is an architectural blueprint for a drone. An object is the physical drone built from that blueprint. Constructor promotion is an automated assembly line that installs the camera and battery instantly without tedious manual wiring."

Deep Dive: How It Works

Classes & Instances: class User { ... } defines state and behavior; $user = new User(...) instantiates.

$this Reference: References the active instance context inside member methods ($this->name).

PHP 8 Constructor Promotion: public function __construct(public string $name, public int $age) {} declares and assigns properties automatically in the parameter list.

Destructor: __destruct() executes automatically when an object loses all references or script terminates.

Syntax Blueprint

<?php

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

$u = new User("Alice", "[email protected]");

Use constructor promotion to declare and assign class properties directly in __construct.

Core Rules to Remember

Zero Boilerplate: Constructor promotion eliminates manual property declarations and $this->x = $x assignments.

Object Operator (->): Access properties and invoke methods using the single arrow -> operator ($user->getName()).

Readonly Properties (PHP 8.1): public readonly string $id prevents modification after initialization.

Common Beginner Traps & How to Fix Them

Mistake:Using $this->$property instead of $this->property.

Why it happens: Adding the extra $ attempts dynamic variable-property evaluation, leading to undefined property notices.

How to fix: Omit the dollar sign after the object operator: $this->property.

Pro Tip: Mark entire classes as readonly (readonly class UserDto {}) in PHP 8.2+ to enforce immutability across all properties.

Live Interactive Example

Hit Run Code to see it live

Constructor Promotion & Method Invocation

PHP 8.2 / CLI

Output Console

Click "Run Code" to view the rendered output.

How it works: Constructor promotion created and populated title, price, and default stock properties.

Your Turn: Micro Challenge

No pressure! Edit the starter code below and test your solution with instant feedback.

Micro Exercise

Create a ServerNode Class

Create a class ServerNode with promoted properties public string $host and public int $port = 8080.
Add a method getEndpoint(): string returning "$this->host:$this->port".
In main, instantiate $node = new ServerNode("api.zencompiler.com", 9000).
Print "Endpoint: " followed by $node->getEndpoint().

Sandbox Output

Click "Run & Check" to test your solution.

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