PHP Functions Classes Methods Confusion

Question

I am working on some legacy code at the moment and stumbled across a weird class/function call that php.net doesn't seem to explain and I've never seen before:

if(security::instance()->check_client()) {

There is a class security, and there are functions named instance and check_client inside that class. But this seems to call two functions in one statement and pass the one to the other, or at least thats what the outcome suggests. Can someone clarify this one for me?

The static keyword (used for static functions) is explained in the PHP Manual. — hakre
– hakre, Commented Sep 16, 2011 at 9:32

naivists · Accepted Answer · 2011-09-16 09:24:03Z

3

The execution goes like this:

first, the static method instance() of the security class is executed
it returns an instance of the security class (most likely)
then, the check_client method is executed on the returned object

So, since security::instance() is an object, you can call a method on it.

answered Sep 16, 2011 at 9:24

naivists

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2 Comments

hakre Over a year ago

How do you know it returns an instance of the security class? :)

naivists Over a year ago

That was just a guess, based on OPs statement that a method check_client exists in the code

Alfwed · Accepted Answer · 2011-09-16 09:29:36Z

1

This is a classical implementation of the singleton pattern

I suppose your class security looks like this :

class security {
    private static $instance = null;

    private function __construct() {}        

    public static function instance() {
        if (null === self::$instance)
            self::$instance = new security();

        return self::$instance;
    }

    public function check_client() { /* do something */ }
}

What it does is that the static method instance returns an instance of the class security; Which mean that security::instance() instanceof security === true

That's why you can chain the call to the check_client() method as in your exemple

security::instance()->check_client()

This is similar to

$secu = security::instance();
$secu->check_client();

answered Sep 16, 2011 at 9:29

Alfwed

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1 Comment

Marius Over a year ago

Hi Alfwed, thank you very much for this thorough explanation.

Peter Porfy · Accepted Answer · 2011-09-16 09:25:45Z

1

security:instance()

is a static call (so probably a static method)

http://php.net/manual/en/language.oop5.static.php

which returns an instance of some class, which has a member method check_client()

so it returns an object, then you can call any public method on that object.

answered Sep 16, 2011 at 9:25

Peter Porfy

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Comments

hakre · Accepted Answer · 2011-09-16 09:26:00Z

0

I can only assume (as I don't know the underlying code), but it might explain it to you.

First of all functions can return objects. You then call an objects function on the returned object:

security::instance()->check_client()

Is the same like:

$securityInstance = security::instance();
$securityInstance->check_client();

Next to that, by the naming of instance I would assume that security::instance() returns the instance of the a security class, probably a singleton implementation or a factory based on the applications configuration.

answered Sep 16, 2011 at 9:26

hakre

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