PHP Functions Classes Methods Confusion

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. C开发者_如何学JAVAan someone clarify this one for me?

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.

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();

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.

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.