What does new self(); mean in PHP?
class, php, self
Solution
`self` points to the class in which it is written.
So, if your getInstance method is in a class name `MyClass`, the following line :
self::$_instance = new self();
Will do the same as :
self::$_instance = new MyClass();
Edit : a bit more information, after the comments.
If you have two classes that extend each other, you have two situations :
- `getInstance` is defined in the child class
- `getInstance` is defined in the parent class
The first situation would look like this (I've removed all non-necessary code, for this example -- you'll have to add it back to get the singleton behavior)* :
class MyParentClass {
}
class MyChildClass extends MyParentClass {
public static function getInstance() {
return new self();
}
}
$a = MyChildClass::getInstance();
var_dump($a);
Here, you'll get :
object(MyChildClass)#1 (0) { }
Which means `self` means `MyChildClass` -- i.e. the class in which it is written.
For the second situation, the code would look like this :
class MyParentClass {
public static function getInstance() {
return new self();
}
}
class MyChildClass extends MyParentClass {
}
$a = MyChildClass::getInstance();
var_dump($a);
And you'd get this kind of output :
object(MyParentClass)#1 (0) { }
Which means `self` means `MyParentClass` -- i.e. here too, the class in which it is written.
With PHP That's why PHP 5.3 introduces a new usage for the `static` keyword : it can now be used exactly where we used `self` in those examples :
class MyParentClass {
public static function getInstance() {
return new static();
}
}
class MyChildClass extends MyParentClass {
}
$a = MyChildClass::getInstance();
var_dump($a);
But, with `static` instead of `self`, you'll now get :
object(MyChildClass)#1 (0) { }
Which means that `static` sort of points to the class that is used (we used `MyChildClass::getInstance()`), and not the one in which it is written.
Of course, the behavior of `self` has not been changed, to not break existing applications -- PHP 5.3 just added a new behavior, recycling the `static` keyword.
And, speaking about PHP 5.3, you might want to take a look at the [Late Static Bindings][1] page of the PHP manual.
Problem
I've never seen code like this: ``` public static function getInstance() { if ( ! isset(self::$_instance)) { self::$_instance = new self(); } return self::$_instance; } ``` Is it the same as `new className()` ? EDIT If the class is inheritant,which class does it point to?