Constructors and Destructors
Constructor
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
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";
}
function __destruct() {
print "Destroying " . __CLASS__ . "\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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Document created the 30/01/2003, last modified the 26/10/2018
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References
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