PHP Cookbook

Chapter 8. Classes and Objects

The earliest versions of PHP didn’t support class definition or object orientation. PHP 4 was the first real attempt at an object interface.¹ It wasn’t until PHP 5, though, that developers had the complex object interfaces they know and use today.

Classes are defined using the class keyword followed by a full description of the constants, properties, and methods inherent to the class. Example 8-1 introduces a basic class construct in PHP, complete with a scoped constant value, a property, and callable methods.

Example 8-1. Basic PHP class with properties and methods

class Foo
{
    const SOME_CONSTANT = 42;

    public string $hello = 'hello';

    public function __construct(public string $world = 'world') {}

    public function greet(): void
    {
        echo sprintf('%s %s', $this->hello, $this->world);
    }
}

An object can be instantiated with the new keyword and the name of the class; instantiation looks somewhat like a function call. Any parameters passed into this instantiation are transparently passed into the class constructor (the __construct() method) to define the object’s initial state. Example 8-2 illustrates how the class definition from Example 8-1 could be instantiated either with or without default property values.

Example 8-2. Instantiating a basic PHP class

$first = new Foo; 
$second = new Foo('universe'); 

$first->greet(); 
$second->greet(); 

echo Foo::SOME_CONSTANT ...