Magic methods in PHP

PHP functions that start with a double underscore – a “__” – are called magic functions (and/or methods) in PHP. 

Magic methods are functions that are always defined inside classes, and are not stand-alone (outside of classes) functions. 

The magic functions available in PHP are: 
__construct(),
 __destruct(),
 __call(),
 __callStatic(),
 __get(),
 __set(),
 __isset(),
 __unset(),
 __sleep(), 
 __wakeup(),
 __toString(),
 __invoke(),
 __set_state(),
 __clone(), and 
 __autoload()

Why are they called magic functions?

PHP does not provide the definitions of the magic functions – the programmer must actually write the code that defines what the magic function will do. 

But, magic functions will never directly be called by the programmer – actually, PHP will call the function ‘behind the scenes’. 

This is why they are called ‘magic’ functions – because they are never directly called, and they allow the programmer to do some pretty powerful things. 

Confused? An example will help make this clear.

Example of using the __construct() magic function in PHP

The most commonly used magic function is __construct(). 
This is because as of PHP version 5, the __construct method is basically the constructor for your class. 

If PHP 5 can not find the __construct() function for a given class, then it will search for a function with the same name as the class name – this is the old way of writing constructors in PHP, where you would just define a function with the same name as the class.

Now, here is an example of a class with the __construct() magic function:

class Animal {
        public $height;      // height of animal  
        public $weight;     // weight of animal

         public function __construct($height, $weight) 
        {
                 $this->height = $height;  //set the height instance variable
                 $this->weight = $weight; //set the weight instance variable
        }
}

In the code above, we have a simple __construct function defined that just sets the height and weight of an animal object. 

So let’s say that we create an object of the Animal class with this code:

Animal obj = new Animal(5, 150);

What happens when we run the code above? 

Well, a call to the __construct() function is made because that is the constructor in PHP 5. 

And the obj object will be an object of the Animal class with a height of 5 and a weight of 150. So, the __construct function is called behind the scenes. Magical, isn’t it?