PHP magic methods

PHP magic methods

Summary: in this tutorial, we will introduce you some important PHP magic methods that you can use to deal with accessing the non-existent members and methods.

PHP __get() and __set() methods

PHP provides a pair of magic methods that deal with non-existent or private property access:

• The __get() method is called whenever you attempt to read a non-existing or private property of an object.
• The __set() method is called whenever you attempt to write to a non-existing or private property of an object.

Let’s take a look at the following example:

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<?php   class Person{ private $firstName;   public function __get($propertyName){ echo "attempted to read non-existing property: $propertyName "; } public function __set($propertyNane, $propertyValue){ echo "attempted to write to non-existing property: $propertyNane "; }   }   $p = new Person();   $p->firstName = 'Doe'; echo $p->firstName;   $p->lastName = 'John'; echo $p->lastName;

How it works.

• First, we attempted to write and read a private property: $firstName.  The method __get()and __set() methods are called automatically.
• Second, we attempted to write and read a non-existing property: $lastName. The method__get() and __set() methods are also called automatically.

The __get() and __set() methods are used to define properties of a class as an associative array instead of separate properties. The following example demonstrates the idea:

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<?php   class Person{ private $properties;   public function __get($propertyName){ if(array_key_exists($propertyName, $properties)){ return $this->properties[$propertyName]; }   } public function __set($propertyNane, $propertyValue){ $this->properties[$propertyNane] = $propertyValue; }   }   $p = new Person(); $p->lastName = 'John'; $p->firstName = 'Doe';   var_dump($p);

By using the __get() and __set() method, the Person class can hold any number of  “virtual” properties.

PHP __call() method

Similar to the __get() and __set() methods, the __call() magic method is called automatically when a nonexistent method of the class is called. The __call() method is rarely used in practice. It is useful when you to create a wrapper class that wraps the existing APIs.

The following example illustrates a simple string class that supports three methods: strlen(), strtoupper() and strtolower().

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<?php   class CString{ private $str = '';   private $APIs = array('strlen','strtoupper','strtolower');   public function __construct($str){ $this->str = $str;   } public function __call($method,$args){ if(in_array($method, $this->APIs)){ array_unshift($args, $this->str); return call_user_func_array($method, $args); }else{ die('Error: call to unsupported method: ' . $method); } } }   $str = new CString('This is a string object'); echo $str->strlen() . ' '; echo $str->strtoupper() . ' '; echo $str->strtolower() . ' ';   echo $str->len(); // Error: call to unsupported method: len

How it works.

• Whenever you call a nonexistent method, the __call() method is called automatically. Inside the __call() method, we check to see if the calling method is supported, which is defined in the $APIs array. If it is, we execute the corresponding string function, otherwise, we issue a message.

PHP uses double underscores ( __ )  as a prefix for the magic methods in the class so it is recommended that you should not use the method name that begins with double underscores ( __ ).

Notice that the constructor and destructor methods ( __construct() and __destruct() ) are also magic methods. For other magic methods, check it out the PHP magic methods.

In this tutorial, you have learned how to use three PHP magic methods:__get() __set() and__call() that deals with non-existent members and methods of a class.