CODEWITHSUNDEEP
phpoopsingleton
BentCoder
BentCoder

Reputation: 12740

OOP singleton validation to see it doesn't create more than 1 instance

I've created Singleton class below but how do I know that only one instance has been created. How do I test it? Also, is there any difference between self::$instance = new FileProcessor() and self::$instance = new static() or which one should I use?

Thanks

CLASS

class FileProcessor
{
    protected static $instance = null;

    public static function get_instance()
    {
        if (self::$instance === null)
        {
            self::$instance = new FileProcessor();
            //self::$instance = new static();
        }

        return self::$instance;
    }
}

$obj_1 = FileProcessor::get_instance();
echo '<pre>'; print_r($obj_1);

$obj_2 = FileProcessor::get_instance();
echo '<pre>'; print_r($obj_2);

OUTPUT

FileProcessor Object
(
)
FileProcessor Object
(
)

Upvotes: 0

Views: 205

Answers (3)

Ulan Murzatayev
Ulan Murzatayev

Reputation: 870

You can compare the result by using === operator. In your case: $obj_1 === $obj_2 will return true if both objects refer to the same instance. More info here: http://www.php.net/manual/en/language.oop5.object-comparison.php. And also here is a good explanation of using new static() : New self vs. new static

Upvotes: 1

deceze
deceze

Reputation: 522372

Ideally you wouldn't be using a singleton pattern to begin with. Instead you dependency inject an instance of FileProcessor to everything that needs it. That means all the places in your app which need FileProcessor don't "get it themselves", rather they receive it from a higher authority. Instead of:

function foo() {
    $fp = FileProcessor::getInstance();
    ...
}

you do:

function foo(FileProcessor $fp) {
    ...
}

This allows you to instantiate exactly one FileProcessor and inject it everywhere it's needed. This gives you full control over its use. You can couple this with a registry/dependency injection container pattern to make managing dependencies easier.

Upvotes: 2

user3383116
user3383116

Reputation: 392

var_dump function allows you to view the contents of the object. This code demonstrates that the objects are really the same:

<?php
class FileProcessor
{
    protected static $instance = null;
    private $arr = array();

    public static function get_instance()
    {
        if (self::$instance === null)
        {
            self::$instance = new FileProcessor();
            //self::$instance = new static();
        }

        return self::$instance;
    }

    public function set($key, $value)
    {
    $this->arr[$key] = $value;
    }
}

$obj_1 = FileProcessor::get_instance();
$obj_1->set('this-is-key', 'this-is-value');
echo '<pre>'; var_dump($obj_1);

$obj_2 = FileProcessor::get_instance();
echo '<pre>'; var_dump($obj_2);

Upvotes: 1

Related Questions