PHP 8 Constructor Property Promotion: Simplifying Class Definitions with Examples

PHP 8, released in November 2020, introduced several features that significantly improve the language’s syntax, performance, and maintainability. One of these features is Constructor Property Promotion, a syntactical addition that simplifies the process of declaring and initializing class properties in constructor methods. In this article, we will explore the benefits of this functionality and examine some examples to illustrate its usage.

Understanding Constructor Property Promotion

In earlier versions of PHP, developers had to write repetitive boilerplate code to define class properties, set their visibility, and initialize them in the constructor method. PHP 8’s Constructor Property Promotion streamlines this process, allowing developers to define properties and their visibility directly within the constructor’s parameter list, significantly reducing the amount of code required.

Example 1: Without Constructor Property Promotion

Consider a simple “Person” class without the use of Constructor Property Promotion:

class Person {
    private string $name;
    private int $age;
    
    public function __construct(string $name, int $age) {
        $this->name = $name;
        $this->age = $age;
    }
}

The class has two properties, $name and $age, which are defined with their respective types and visibility. They are then initialized in the constructor method.

Example 2: Using Constructor Property Promotion

Now let’s rewrite the same “Person” class using Constructor Property Promotion:

class Person {
    public function __construct(private string $name, private int $age) {}
}

As you can see, the class definition is now more concise. We have defined the properties and their visibility directly within the constructor’s parameter list, eliminating the need to write separate property declarations and assignments.

Example 3: Mixing Promoted and Non-Promoted Properties

Constructor Property Promotion can be used alongside non-promoted properties for flexibility in class definitions:

class Employee {
    private float $salary;
    
    public function __construct(private string $name, private int $age, float $salary) {
        $this->salary = $salary;
    }
}

In this “Employee” class, the $name and $age properties use Constructor Property Promotion, while the $salary property is declared and initialized in the traditional manner.

PHP 8’s Constructor Property Promotion functionality helps developers simplify their code by reducing the amount of boilerplate required to define and initialize class properties. This feature makes PHP classes more readable and maintainable, encouraging better coding practices and improving developer productivity.