Are Singletons Really Necessary for PHP Database Access?

Singletons: A Myth in PHP Database Access

You're questioning the necessity of singletons for PHP database access, considering the following simplified singleton class:

class Database {
    private static $db;

    private function __construct(){}

    static function get() {
        if(!isset(self::$db))
            self::$db = new PDO(...);

        return self::$db;
    }
}

You wonder why this wouldn't suffice instead of a more complex singleton class with a singleton() method.

Debunking the Usefulness of Singletons in PHP

In PHP, singletons offer minimal to no advantages:

• Memory Conservation: Singletons aim to reduce memory usage by sharing instances in shared memory. However, in PHP, objects reside in private request memory, rendering this purpose irrelevant.
• Enforcing Singleton: Conceptual singletons may not require language mechanisms for enforcement. Only consider singletons when creating a second instance will cause detrimental effects.

Disadvantages of Singletons

• Global Coupling: Singletons introduce global scope dependencies, complicating testing and maintainability.
• Dependency Injection Alternative: When a single instance is required across multiple classes, dependency injection provides a cleaner and more testable solution.

Erich Gamma's Skepticism

Even one of the creators of the singleton pattern, Erich Gamma, now questions its usefulness:

• "I'm in favor of dropping Singleton. Its use is almost always a design smell"

When Singletons Might be Applicable

Despite the general skepticism towards singletons in PHP, consider these scenarios:

• Global Access Point: Creating a global access point for an instance within the same request MAY be justified, but can introduce coupling and maintenance challenges.
• Eliminating Second Instances: Only implement singletons when there's a dire need to prevent additional instances from being created.

Additional Resources

• [Testing Singletons in PHP: Why it's Tricky](link_to_How_is_testing_the_registry_pattern_or_singleton_hard_in_PHP)
• [Disadvantages of Singleton Database Classes](link_to_What_are_the_disadvantages_of_using_a_PHP_database_class_as_a_singleton)
• [Decision Diagram for Singletons](link_to_Singleton_Decision_Diagram)

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