No $this In Static Methods

Static methods are a special type of methods : they may be called without instantiating the class into an object. This makes them convenient for various tasks that are common to all objects from a class.

However, since they may be called without instantiation, this means that the special variable $this, which typically represents the current object, may be unavailable.

PHP doesn't check for $this usage inside static methods at compile time. At execution time, it will raise an error, since it can't find any value for $this.

It is recommended to check that static methods have no usage of $this.

Rule Details

This rule require that every static method makes no use of the $this variable. The following patterns are considered warnings:

<?php

class x {
	static function y() {
		$this->callMethod();
		return $this->property;
	}
}

?>

The following code is considered legit :

<?php

class x {
	static function y() {
		self::callStaticMethod();
		return self::$staticProperty;
	}
}


?>

When Not To Use It

This is not checked by PHP but will lead to bugs.

Further Reading

• Static Keyword