Behaviour of private constructor in singleton design pattern in PHP

Question

Consider this example singleton class:

class Model_Acl
{
    protected static $_instance;

    private function __construct($a) {
        echo $a;
    }

    public static function getInstance()
    {
        if(!isset(self::$_instance)) {
            self::$_instance = new Model_Acl('hello world');
        }
        return self::$_instance;
    }
}

In the static method of the same class, I am able to initialize the class to which constructor is private. Does that mean the scope of class initialization becomes local when trying to instantiate object within the class?

I will appreciate if someone could explain the behaviour of PHP when it comes to class instantiation with reference to access modifiers.

score 4 · Accepted Answer · edited May 23 '17 at 12:31

4

You can only initialize it thru Model_Acl::getinstance().

But yes, it will work.

Singleton is not considered a good practice, you should consider Dependency Injection.

http://fabien.potencier.org/article/11/what-is-dependency-injection.

More information about php Singletons

Best practice on PHP singleton classes

edited May 23 '17 at 12:31

Community

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answered Feb 05 '13 at 06:18

Danilo Kobold

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Singletons are not considered good practice in *most* applications. They can be good though, such as for a data abstraction layer. – Adi Bradfield Jun 05 '15 at 23:12

Behaviour of private constructor in singleton design pattern in PHP

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