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PHP

Constructors and Destructors


Constructors and Destructors

Constructor

void __construct ([ mixed $args [, $... ]] )

PHP 5 allows developers to declare constructor methods for classes. Classes which have a constructor method call this method on each newly-created object, so it is suitable for any initialization that the object may need before it is used.

Note: Parent constructors are not called implicitly if the child class defines a constructor. In order to run a parent constructor, a call to parent::__construct() within the child constructor is required.

Example #1 using new unified constructors

<?php
class BaseClass {
   function 
__construct() {
       print 
"In BaseClass constructor\n";
   }
}

class 
SubClass extends BaseClass {
   function 
__construct() {
       
parent::__construct();
       print 
"In SubClass constructor\n";
   }
}

$obj = new BaseClass();
$obj = new SubClass();
?>

For backwards compatibility, if PHP 5 cannot find a __construct() function for a given class, it will search for the old-style constructor function, by the name of the class. Effectively, it means that the only case that would have compatibility issues is if the class had a method named __construct() which was used for different semantics.

Unlike with other methods, PHP will not generate an E_STRICT level error message when __construct() is overridden with different parameters than the parent __construct() method has.

As of PHP 5.3.3, methods with the same name as the last element of a namespaced class name will no longer be treated as constructor. This change doesn't affect non-namespaced classes.

Example #2 Constructors in namespaced classes

<?php
namespace Foo;
class 
Bar {
    public function 
Bar() {
        
// treated as constructor in PHP 5.3.0-5.3.2
        // treated as regular method as of PHP 5.3.3
    
}
}
?>

Destructor

void __destruct ( void )

PHP 5 introduces a destructor concept similar to that of other object-oriented languages, such as C++. The destructor method will be called as soon as there are no other references to a particular object, or in any order during the shutdown sequence.

Example #3 Destructor Example

<?php
class MyDestructableClass {
   function 
__construct() {
       print 
"In constructor\n";
       
$this->name "MyDestructableClass";
   }

   function 
__destruct() {
       print 
"Destroying " $this->name "\n";
   }
}

$obj = new MyDestructableClass();
?>

Like constructors, parent destructors will not be called implicitly by the engine. In order to run a parent destructor, one would have to explicitly call parent::__destruct() in the destructor body.

The destructor will be called even if script execution is stopped using exit(). Calling exit() in a destructor will prevent the remaining shutdown routines from executing.

Note:

Destructors called during the script shutdown have HTTP headers already sent. The working directory in the script shutdown phase can be different with some SAPIs (e.g. Apache).

Note:

Attempting to throw an exception from a destructor (called in the time of script termination) causes a fatal error.



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