Php Magic Methods – __isset() and __unset()

In previous PHP5 OOPS tutorial on PHP5 Tutorial – Magic Methods – __get() and __set(), we learnt how and when to use these magic methods.

This PHP5 OOPS tutorial will teach you how and when to use the magic methods __isset() and __unset().

These methods are automatically called internally when isset() and unset() is called on undeclared data members. The magic method __isset() method receives an argument – the value of which is the name of the variable that the program wants to test if the variable is set or not.

The magic method __unset() method receives an argument – the value of which is the name of the variable that the program wants to unset.

Look at the example below:

class Customer {
 private $data = array();
 
 public function __set($dt, $vl) {
  $this->data[$dt] = $vl;
 }
 
 public function __get($dt) {
  return $this->data[$dt];
 }
 
 public function __isset($dt) {
  return isset($this->data[$dt]);
 }
 
 public function __unset($dt) {
  return unset($this->data[$dt]);
 }
}
 
$c = new Customer();
$c->name = "Hiren Prajapati";
 
echo isset($c->name)."\n";
echo unset($c->name);

In the above example the script creates a new Customer Object. The program assigns a string value to an undeclared variable i.e. $c->name. The undeclared variable is handled by the magic method __set(). Read this post on PHP5 Magic Methods __set() if you need more understanding how the magic method __set() works.
The program ties to check if the undeclared variable i.e., $c->name has been set or not using the PHP method isset(). Since $c->name is an undeclared variable the PHP5 magic method __isset() is invoked that takes the name of the undeclared variable i.e. “name” and checks if the internal array $data["name"] is set or not.

Similarly, when the program calls unset() on the undeclared variable i.e. $c->name, the PHP5 magic method __unset() is invoked that takes the name of the undeclared variable i.e. “name” and unsets the internal array $data["name"].