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. If the child does not define a constructor then it may be inherited from the parent class just like a normal class method (if it was not declared as private).
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"; } } class OtherSubClass extends BaseClass { // inherits BaseClass's constructor } // In BaseClass constructor $obj = new BaseClass(); // In BaseClass constructor // In SubClass constructor $obj = new SubClass(); // In BaseClass constructor $obj = new OtherSubClass(); ?>
For backwards compatibility with PHP 3 and 4, if PHP 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.
Old style constructors are DEPRECATED in PHP 7.0, and will be removed in a future version. You should always use __construct() in new code.
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. Also like constructors, a child class may inherit the parent's destructor if it does not implement one itself.
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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https://secure.php.net/manual/en/language.oop5.decon.php