Part 4 - Magic Methods in OOP

To make the use of objects easier, PHP also provides a number of magic methods, or special methods that are called when certain common actions occur within objects. This allows developers to perform a number of useful tasks with relative ease.

Using Constructors and Destructors

When an object is instantiated, it's often desirable to set a few things right off the bat. To handle this, PHP provides the magic method __construct(), which is called automatically whenever a new object is
created.

For the purpose of illustrating the concept of constructors, add a constructor to MyClass that will output a message whenever a new instance of the class is created:

<?php

class MyClass

{

  public $prop1 = "I'm a class property!";

  public function __construct()

  {

      echo 'The class "', __CLASS__, '" was initiated!<br />';

  }

  public function setProperty($newval)

  {

      $this->prop1 = $newval;

  }

  public function getProperty()

  {

      return $this->prop1 . "<br />";

  }

}

// Create a new object

$obj = new MyClass;

// Get the value of $prop1

echo $obj->getProperty();

// Output a message at the end of the file

echo "End of file.<br />";

?>

Note — __CLASS__ returns the name of the class in which it is called; this is what is known as a magic constant. There are several available magic constants, which you can read more about in the PHP manual.

Reloading the file in your browser will produce the following result:

The class "MyClass" was initiated!

I'm a class property!

End of file.

To call a function when the object is destroyed, the __destruct() magic method is available. This is useful for class cleanup (closing a database connection, for instance).

Output a message when the object is destroyed by defining the magic method
__destruct() in MyClass:

<?php

class MyClass

{

  public $prop1 = "I'm a class property!";

  public function __construct()

  {

      echo 'The class "', __CLASS__, '" was initiated!<br />';

  }

  public function __destruct()

  {

      echo 'The class "', __CLASS__, '" was destroyed.<br />';

  }

  public function setProperty($newval)

  {

      $this->prop1 = $newval;

  }

  public function getProperty()

  {

      return $this->prop1 . "<br />";

  }

}

// Create a new object

$obj = new MyClass;

// Get the value of $prop1

echo $obj->getProperty();

// Output a message at the end of the file

echo "End of file.<br />";

?>

With a destructor defined, reloading the test file results in the following output:

The class "MyClass" was initiated!

I'm a class property!

End of file.

The class "MyClass" was destroyed.

"When the end of a file is reached, PHP automatically releases all resources."

To explicitly trigger the destructor, you can destroy the object using the
function unset():

<?php

class MyClass

{

  public $prop1 = "I'm a class property!";

  public function __construct()

  {

      echo 'The class "', __CLASS__, '" was initiated!<br />';

  }

  public function __destruct()

  {

      echo 'The class "', __CLASS__, '" was destroyed.<br />';

  }

  public function setProperty($newval)

  {

      $this->prop1 = $newval;

  }

  public function getProperty()

  {

      return $this->prop1 . "<br />";

  }

}

// Create a new object

$obj = new MyClass;

// Get the value of $prop1

echo $obj->getProperty();

// Destroy the object

unset($obj);

// Output a message at the end of the file

echo "End of file.<br />";

?>

Now the result changes to the following when loaded in your browser:

The class "MyClass" was initiated!

I'm a class property!

The class "MyClass" was destroyed.

End of file.

Converting to a String

To avoid an error if a script attempts to output MyClass as a string, another magic method is used called __toString().

Without __toString(), attempting to output the object as a string results in a fatal error. Attempt to use echo to output the object without a magic method in place:

<?php

class MyClass

{

  public $prop1 = "I'm a class property!";

  public function __construct()

  {

      echo 'The class "', __CLASS__, '" was initiated!<br />';

  }

  public function __destruct()

  {

      echo 'The class "', __CLASS__, '" was destroyed.<br />';

  }

  public function setProperty($newval)

  {

      $this->prop1 = $newval;

  }

  public function getProperty()

  {

      return $this->prop1 . "<br />";

  }

}

// Create a new object

$obj = new MyClass;

// Output the object as a string

echo $obj;

// Destroy the object

unset($obj);

// Output a message at the end of the file

echo "End of file.<br />";

?>

This results in the following:

The class "MyClass" was initiated!

Catchable fatal error: Object of class MyClass could not be converted to string in /Applications/XAMPP/xamppfiles/htdocs/testing/test.php on line 40

To avoid this error, add a __toString() method:

<?php

class MyClass

{

  public $prop1 = "I'm a class property!";

  public function __construct()

  {

      echo 'The class "', __CLASS__, '" was initiated!<br />';

  }

  public function __destruct()

  {

      echo 'The class "', __CLASS__, '" was destroyed.<br />';

  }

  public function __toString()

  {

      echo "Using the toString method: ";

      return $this->getProperty();

  }

  public function setProperty($newval)

  {

      $this->prop1 = $newval;

  }

  public function getProperty()

  {

      return $this->prop1 . "<br />";

  }

}

// Create a new object

$obj = new MyClass;

// Output the object as a string

echo $obj;

// Destroy the object

unset($obj);

// Output a message at the end of the file

echo "End of file.<br />";

?>

In this case, attempting to convert the object to a string results in a call to the getProperty() method. Load the test script in your browser to see the result:

The class "MyClass" was initiated!

Using the toString method: I'm a class property!

The class "MyClass" was destroyed.

End of file.

Tip — In addition to the magic methods discussed in this section, several others are available. For a complete list of magic methods, see the PHP manual page.




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