PHP 5 OOP Revolution — Objects by Reference

Also Known As

TL;DR

Explanation

PHP 4 passed objects by value like any other variable, meaning every function call or assignment copied the entire object. PHP 5 (2004) introduced a handle-based object model: variables hold a reference to an object, not a copy. PHP 5 also added interfaces, abstract classes, public/protected/private visibility, static methods and properties, __autoload, exceptions, and type hints for objects and arrays. This was the release that made PHP viable for enterprise-scale applications and frameworks like Symfony and Zend Framework.

Common Misconception

Why It Matters

Common Mistakes

• Assuming PHP always passed objects by reference
• Confusing passed by handle with passed by reference — clone() still creates a copy
• Not realising PHP 4 OOP limitations explain the procedural-heavy codebase you just inherited

Code Examples

// PHP 4 OOP — no visibility, no type hints, pass by value:
class User {
    var $name; // No visibility
    function getName() { return $this->name; } // No return type
}

// PHP 5+ proper OOP:
class User {
    public function __construct(
        private readonly string $name,
        private readonly string $email,
    ) {}

    public function getName(): string { return $this->name; }
    public function getEmail(): string { return $this->email; }
}

References

• ↗ https://www.php.net/manual/en/language.oop5.php

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