Use $this to refer to the current object. Use self to refer to the current class. In other words, use $this->member for non-static members, use self::$member for static members.
In the example below, sayHello() and sayGoodbye() are using self and $this difference can be observed here.
class Person {
private $name;
public function __construct($name) {
$this->name = $name;
}
public function getName() {
return $this->name;
}
public function getTitle() {
return $this->getName()." the person";
}
public function sayHello() {
echo "Hello, I'm ".$this->getTitle()."<br/>";
}
public function sayGoodbye() {
echo "Goodbye from ".self::getTitle()."<br/>";
}
}
class Geek extends Person {
public function __construct($name) {
parent::__construct($name);
}
public function getTitle() {
return $this->getName()." the geek";
}
}
$geekObj = new Geek("Ludwig");
$geekObj->sayHello();
$geekObj->sayGoodbye();
static refers to whatever class in the hierarchy you called the method on. It allows for better reuse of static class properties when classes are inherited.
Consider the following code:
class Car {
protected static $brand = 'unknown';
public static function brand() {
return self::$brand."\\n";
}
}
class Mercedes extends Car {
protected static $brand = 'Mercedes';
}
class BMW extends Car {
protected static $brand = 'BMW';
}
echo (new Car)->brand();
echo (new BMW)->brand();
echo (new Mercedes)->brand();
This doesn’t produce the result you want:
unknown
unknown
unknown
That’s because self refers to the Car class whenever method brand() is called.
To refer to the correct class, you need to use static instead:
class Car {
protected static $brand = 'unknown';
public static function brand() {
return static::$brand."\\n";
}
}
class Mercedes extends Car {
protected static $brand = 'Mercedes';
}
class BMW extends Car {
protected static $brand = 'BMW';
}
echo (new Car)->brand();
echo (new BMW)->brand();
echo (new Mercedes)->brand();
This does produce the desired output:
unknown
BMW
Mercedes