A DRY implementation for the Singleton design pattern in PHP.

Singleton.php

<?php

trait Singleton
{
    /**
     * The instance of our Singleton object.
     */
    protected static $instance;

    /**
     * The public method to return an instance of the Singleton object.
     *
     * @return void
     */
    public static function getInstance()
    {
        if (null === static::$instance)
        {
            static::$instance = new static();
        }

        return static::$instance;
    }

    /**
     * Make sure the constructor is protected so we can't accidentally create
     * a new instance of the object.
     *
     * @return void
     */
    protected function __construct()
    {

    }

    /**
     * Disable external usage of __clone() to return a new instance.
     */
    private function __clone()
    {

    }

    /**
     * Disable external usage of __wakeup() to return a new instance.
     */
    private function __wakeup()
    {

    }
}

Implementation is pretty simple at this point:

<?php

class Example
{
    use Singleton; // assume autoloader exists

    protected function __construct()
    {
        // you can still implement your constructor. 
        // it's just protected to avoid accidental instantiation.
    }
}

You can now get the object instance via the public Singleton getInstance() method.

<?php

$example = Example::getInstance();

That's it! Enjoy an easy way to implement the Singleton design pattern without repeating code.