Constructor Promotion (8.0)

Part of the Object Oriented Programming section of Coddy's PHP journey — lesson 42 of 91.

PHP 8.0 introduced constructor promotion, a feature that dramatically reduces boilerplate code when defining classes. Instead of declaring properties separately and then assigning them in the constructor, you can do both in one step.

Here's the traditional approach you've been using:

<?php
class Product {
    private string $name;
    private float $price;
    
    public function __construct(string $name, float $price) {
        $this->name = $name;
        $this->price = $price;
    }
    
    public function getInfo(): string {
        return $this->name . ": $" . $this->price;
    }
}

With constructor promotion, you add the access modifier directly to the constructor parameters:

<?php
class Product {
    public function __construct(
        private string $name,
        private float $price
    ) {}
    
    public function getInfo(): string {
        return $this->name . ": $" . $this->price;
    }
}

$product = new Product("Laptop", 999.99);
echo $product->getInfo();

Output:

Laptop: $999.99

By adding private, protected, or public before a constructor parameter, PHP automatically creates the property and assigns the value. You can mix promoted and regular parameters in the same constructor, and you can still add logic inside the constructor body if needed.

Key Point: Constructor promotion eliminates repetitive property declarations and assignments, making your classes cleaner and easier to read while maintaining full encapsulation control.

Challenge

Easy

Let's build a contact management system that showcases the elegance of constructor promotion. You'll create a clean, modern PHP class that eliminates boilerplate code while maintaining proper encapsulation.

You'll organize your code across two files:

Contact.php — Create a Contact class using constructor promotion to define all properties directly in the constructor signature. Your contact should have:
- A private $name property (string)
- A private $email property (string)
- A private $phone property (string) with a default value of "Not provided"
Use constructor promotion syntax — no separate property declarations needed! Add a public method getFullDetails() that returns "[name] | [email] | [phone]". Also add a method getSummary() that returns "Contact: [name]".
main.php — Include the Contact file. You'll receive three inputs: a name, an email, and a phone number. Create two Contact instances:
- The first contact should use all three values (name, email, and phone)
- The second contact should use only the name and email (relying on the default phone value)
Print four lines:
- The full details of the first contact
- The summary of the first contact
- The full details of the second contact
- The summary of the second contact

Notice how constructor promotion lets you define properties, set their visibility, declare their types, and assign values — all in a single, readable constructor signature. The optional phone parameter with a default value demonstrates that promoted parameters work seamlessly with default values, just like regular parameters.

Cheat sheet

PHP 8.0 introduced constructor promotion, which allows you to declare and initialize class properties directly in the constructor parameters by adding an access modifier.

Traditional approach:

<?php
class Product {
    private string $name;
    private float $price;
    
    public function __construct(string $name, float $price) {
        $this->name = $name;
        $this->price = $price;
    }
}

With constructor promotion:

<?php
class Product {
    public function __construct(
        private string $name,
        private float $price
    ) {}
}

$product = new Product("Laptop", 999.99);

By adding private, protected, or public before a constructor parameter, PHP automatically creates the property and assigns the value.

You can use default values with promoted parameters:

<?php
class Contact {
    public function __construct(
        private string $name,
        private string $email,
        private string $phone = "Not provided"
    ) {}
}

Constructor promotion can be mixed with regular parameters, and you can still add logic inside the constructor body if needed.

Try it yourself

<?php

require_once 'Contact.php';

// Read input
$name = trim(fgets(STDIN));
$email = trim(fgets(STDIN));
$phone = trim(fgets(STDIN));

// TODO: Create first contact with all three values (name, email, phone)

// TODO: Create second contact with only name and email (use default phone)

// TODO: Print full details of first contact

// TODO: Print summary of first contact

// TODO: Print full details of second contact

// TODO: Print summary of second contact

?>

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

Constructor Promotion (8.0)

Cheat sheet

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