Be aware of potential memory leaks caused by circular references within objects. The PHP manual states "[t]he destructor method will be called as soon as all references to a particular object are removed" and this is precisely true: if two objects reference each other (or even if one object has a field that points to itself as in $this->foo = $this) then this reference will prevent the destructor being called even when there are no other references to the object at all. The programmer can no longer access the objects, but they still stay in memory.
Consider the following example:
<?php
header("Content-type: text/plain");
class Foo {
/**
* An indentifier
* @var string
*/
private $name;
/**
* A reference to another Foo object
* @var Foo
*/
private $link;
public function __construct($name) {
$this->name = $name;
}
public function setLink(Foo $link){
$this->link = $link;
}
public function __destruct() {
echo 'Destroying: ', $this->name, PHP_EOL;
}
}
// create two Foo objects:
$foo = new Foo('Foo 1');
$bar = new Foo('Foo 2');
// make them point to each other
$foo->setLink($bar);
$bar->setLink($foo);
// destroy the global references to them
$foo = null;
$bar = null;
// we now have no way to access Foo 1 or Foo 2, so they OUGHT to be __destruct()ed
// but they are not, so we get a memory leak as they are still in memory.
//
// Uncomment the next line to see the difference when explicitly calling the GC:
// gc_collect_cycles();
//
// see also: http://www.php.net/manual/en/features.gc.php
//
// create two more Foo objects, but DO NOT set their internal Foo references
// so nothing except the vars $foo and $bar point to them:
$foo = new Foo('Foo 3');
$bar = new Foo('Foo 4');
// destroy the global references to them
$foo = null;
$bar = null;
// we now have no way to access Foo 3 or Foo 4 and as there are no more references
// to them anywhere, their __destruct() methods are automatically called here,
// BEFORE the next line is executed:
echo 'End of script', PHP_EOL;
?>
This will output:
Destroying: Foo 3
Destroying: Foo 4
End of script
Destroying: Foo 1
Destroying: Foo 2
But if we uncomment the gc_collect_cycles(); function call in the middle of the script, we get:
Destroying: Foo 2
Destroying: Foo 1
Destroying: Foo 3
Destroying: Foo 4
End of script
As may be desired.
NOTE: calling gc_collect_cycles() does have a speed overhead, so only use it if you feel you need to.
생성자와 소멸자
생성자
PHP 5 에서는 클래스의 생성자 메서드를 선언하는것을 허용합니다. 클래스는 새로이 생성된 오브젝트마다 자신의 생성자 메서드를 호출합니다. 그래서, 객체 초기화를 위해 사용할수 있습니다.
Note: 부모 생성자는 자식클래스가 생성자를 가지고 있을경우 내부적으로 호출되지 않습니다. 부모 생성자를 호출하기 위해서는 자식 생성자 내에서 parent::__construct() 호출이 필요합니다. 자식이 생성자를 가지지 않는다면 다른 일반적인 클래스 메서드처럼 부모클래스의 생성자가 상속됩니다(private 메서드는 제외).
Example #1 생성자 사용하기
<?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();
?>
하위 호환성을 위해, PHP 5 가 클래스에서 __construct() 함수를 찾지 못할경우, 그리고, 부모 클래스로부터 상속하지 않은 경우, 클래스이름에 기반한 예전방식의 생성자를 함수를 찾게 될것입니다. 호환성 문제가 생길수 있는 케이스는 클래스가 __construct() 메서드를 가진경우 해당 메서드를 다른 의미로 사용하는 경우 입니다.
다른 메서드와는 다르게, __construct() 가 부모의 __construct()와는 다르게 재정의 되어도
E_STRICT 에러메시지를 발생하지 않습니다.
PHP 5.3.3 이후로 네임스페이스 클래스의 마지막 엘리먼트명을 더이상 생성자로 다루지 않습니다. 이변경은 비네임스페이스 클래스들에게는 영향을 미치지 않습니다.
Example #2 네임스페이스 클래스의 생성자
<?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
}
}
?>
소멸자
void __destruct
( void
)
PHP 5는 C++과 같은 객체지향 언어에 존재하는 비슷한 개념의 소멸자를 선보였습니다. 소멸자 메서드는 더이상 객체를 참조하지 않거나, 종료가 일어나는동안 호출될수 있을 것입니다.
Example #3 소멸자 예제
<?php
class MyDestructableClass {
function __construct() {
print "In constructor\n";
$this->name = "MyDestructableClass";
}
function __destruct() {
print "Destroying " . $this->name . "\n";
}
}
$obj = new MyDestructableClass();
?>
생성자처럼, 부모 소멸자는 묵시적으로 호출되지 않습니다. 부모 소멸자를 호출하기 위해서는, 소멸자 내부에서 parent::__destruct() 를 명시적으로 호출해 줘야 합니다. 또한 생성자처럼, 자식 클래스가 소멸자를 가지지 않는다면 부모의 것을 상속합니다.
소멸자는 exit() 로 스크립트 실행이 중단되더라도 실행됩니다. 소멸자 내부에서 exit() 를 호출 하는 것은 남은 종료 루틴을 막게 됩니다.
Note:
스크립트가 종료되는 동안에 소멸자가 호출된 경우 HTTP 헤더는 이미 보내진 뒤입니다. 스크립트가 종료될때의 작업디렉터리는 SAPI 마다 다를수 있습니다.(예를 들면 Apache)
Note:
소멸자 내부에서 예외를 발생시키려고 시도할경우(스크립트 종료시점) fatal error 를 발생시킵니다.
add a note
User Contributed Notes 12 notes
david dot scourfield at llynfi dot co dot uk ¶
12 years ago
iwwp at outlook dot com ¶
4 years ago
To better understand the __destrust method:
class A {
protected $id;
public function __construct($id)
{
$this->id = $id;
echo "construct {$this->id}\n";
}
public function __destruct()
{
echo "destruct {$this->id}\n";
}
}
$a = new A(1);
echo "-------------\n";
$aa = new A(2);
echo "=============\n";
The output content:
construct 1
-------------
construct 2
=============
destruct 2
destruct 1
domger at freenet dot de ¶
6 years ago
The __destruct magic method must be public.
public function __destruct()
{
;
}
The method will automatically be called externally to the instance. Declaring __destruct as protected or private will result in a warning and the magic method will not be called.
Note: In PHP 5.3.10 i saw strange side effects while some Destructors were declared as protected.
spleen ¶
15 years ago
It's always the easy things that get you -
Being new to OOP, it took me quite a while to figure out that there are TWO underscores in front of the word __construct.
It is __construct
Not _construct
Extremely obvious once you figure it out, but it can be sooo frustrating until you do.
I spent quite a bit of needless time debugging working code.
I even thought about it a few times, thinking it looked a little long in the examples, but at the time that just seemed silly(always thinking "oh somebody would have made that clear if it weren't just a regular underscore...")
All the manuals I looked at, all the tuturials I read, all the examples I browsed through - not once did anybody mention this!
(please don't tell me it's explained somewhere on this page and I just missed it, you'll only add to my pain.)
I hope this helps somebody else!
prieler at abm dot at ¶
16 years ago
i have written a quick example about the order of destructors and shutdown functions in php 5.2.1:
<?php
class destruction {
var $name;
function destruction($name) {
$this->name = $name;
register_shutdown_function(array(&$this, "shutdown"));
}
function shutdown() {
echo 'shutdown: '.$this->name."\n";
}
function __destruct() {
echo 'destruct: '.$this->name."\n";
}
}
$a = new destruction('a: global 1');
function test() {
$b = new destruction('b: func 1');
$c = new destruction('c: func 2');
}
test();
$d = new destruction('d: global 2');
?>
this will output:
shutdown: a: global 1
shutdown: b: func 1
shutdown: c: func 2
shutdown: d: global 2
destruct: b: func 1
destruct: c: func 2
destruct: d: global 2
destruct: a: global 1
conclusions:
destructors are always called on script end.
destructors are called in order of their "context": first functions, then global objects
objects in function context are deleted in order as they are set (older objects first).
objects in global context are deleted in reverse order (older objects last)
shutdown functions are called before the destructors.
shutdown functions are called in there "register" order. ;)
regards, J
Per Persson ¶
11 years ago
As of PHP 5.3.10 destructors are not run on shutdown caused by fatal errors.
For example:
<?php
class Logger
{
protected $rows = array();
public function __destruct()
{
$this->save();
}
public function log($row)
{
$this->rows[] = $row;
}
public function save()
{
echo '<ul>';
foreach ($this->rows as $row)
{
echo '<li>', $row, '</li>';
}
echo '</ul>';
}
}
$logger = new Logger;
$logger->log('Before');
$nonset->foo();
$logger->log('After');
?>
Without the $nonset->foo(); line, Before and After will both be printed, but with the line neither will be printed.
One can however register the destructor or another method as a shutdown function:
<?php
class Logger
{
protected $rows = array();
public function __construct()
{
register_shutdown_function(array($this, '__destruct'));
}
public function __destruct()
{
$this->save();
}
public function log($row)
{
$this->rows[] = $row;
}
public function save()
{
echo '<ul>';
foreach ($this->rows as $row)
{
echo '<li>', $row, '</li>';
}
echo '</ul>';
}
}
$logger = new Logger;
$logger->log('Before');
$nonset->foo();
$logger->log('After');
?>
Now Before will be printed, but not After, so you can see that a shutdown occurred after Before.
Yousef Ismaeil cliprz[At]gmail[Dot]com ¶
10 years ago
<?php
/**
* a funny example Mobile class
*
* @author Yousef Ismaeil Cliprz[At]gmail[Dot]com
*/
class Mobile {
/**
* Some device properties
*
* @var string
* @access public
*/
public $deviceName,$deviceVersion,$deviceColor;
/**
* Set some values for Mobile::properties
*
* @param string device name
* @param string device version
* @param string device color
*/
public function __construct ($name,$version,$color) {
$this->deviceName = $name;
$this->deviceVersion = $version;
$this->deviceColor = $color;
echo "The ".__CLASS__." class is stratup.<br /><br />";
}
/**
* Some Output
*
* @access public
*/
public function printOut () {
echo 'I have a '.$this->deviceName
.' version '.$this->deviceVersion
.' my device color is : '.$this->deviceColor;
}
/**
* Umm only for example we will remove Mobile::$deviceName Hum not unset only to check how __destruct working
*
* @access public
*/
public function __destruct () {
$this->deviceName = 'Removed';
echo '<br /><br />Dumpping Mobile::deviceName to make sure its removed, Olay :';
var_dump($this->deviceName);
echo "<br />The ".__CLASS__." class is shutdown.";
}
}
// Oh ya instance
$mob = new Mobile('iPhone','5','Black');
// print output
$mob->printOut();
?>
The Mobile class is stratup.
I have a iPhone version 5 my device color is : Black
Dumpping Mobile::deviceName to make sure its removed, Olay :
string 'Removed' (length=7)
The Mobile class is shutdown.
instatiendaweb at gmail dot com ¶
3 years ago
/**
* Haciendo una prueba con dos clases y dos destructores
* La prueba consta de acceder a la variable global del primer objeto en el segundo
* objeto el destructor 2
* Primera clase ==> $GLOBALS['obj']
* SEgunda clase ==> $GLOBALS['obj2']
* Se ejecuta construct y todo el codigo....
* Primer destruct borra el objeto y lo hace null
* Tratamos de acceder a $GLOBALS['obj'] en el segundo destruct pero
* ya no esta es un objeto null
* Warning: Undefined array key "obj" in...
*/
class MyDestructableClass{
public $parametro;
function __construct($parametro) {
echo("<div class=\"div\">"), "Construyendo ",__CLASS__ , ("</div>");
escribir::verifacionnota($this ,'Antes de guardar la variable ');
$this->parametro = $parametro;
escribir::verifacionnota($this ,'Despues de guardar la variable ');
}
function __destruct() {
escribir::linea(5); //Separador
echo("<div class=\"div\">"), "Destruyendo " , __CLASS__ , ("</div>");
escribir::verifacionnota($this ,'Antes de borrar la variable ');
unset($this->parametro);
escribir::verifacionnota($this ,'Despues de borrar la variable ');
// unset($GLOBALS[$this]);
}
}
$obj = new MyDestructableClass('parametroone');
escribir::verifacionnota($obj ,' Verificar la clase MyDestructableClass, no es necesario
borrar la clase porque se ejecuta al final del script ');
escribir::titulosep('Provando ejemplo aqui se puede acceder a la variable global');
escribir::verificacion($GLOBALS['obj']);
class destructora{
function __destruct(){
escribir::titulosep('Sin embargo esta variable muere aqui');
escribir::verificacion($GLOBALS['obj']);
}
}
$obj2 = new destructora();
bolshun at mail dot ru ¶
16 years ago
Ensuring that instance of some class will be available in destructor of some other class is easy: just keep a reference to that instance in this other class.
Jonathon Hibbard ¶
14 years ago
Please be aware of when using __destruct() in which you are unsetting variables...
Consider the following code:
<?php
class my_class {
public $error_reporting = false;
function __construct($error_reporting = false) {
$this->error_reporting = $error_reporting;
}
function __destruct() {
if($this->error_reporting === true) $this->show_report();
unset($this->error_reporting);
}
?>
The above will result in an error:
Notice: Undefined property: my_class::$error_reporting in my_class.php on line 10
It appears as though the variable will be unset BEFORE it actually can execute the if statement. Removing the unset will fix this. It's not needed anyways as PHP will release everything anyways, but just in case you run across this, you know why ;)
Reza Mahjourian ¶
17 years ago
Peter has suggested using static methods to compensate for unavailability of multiple constructors in PHP. This works fine for most purposes, but if you have a class hierarchy and want to delegate parts of initialization to the parent class, you can no longer use this scheme. It is because unlike constructors, in a static method you need to do the instantiation yourself. So if you call the parent static method, you will get an object of parent type which you can't continue to initialize with derived class fields.
Imagine you have an Employee class and a derived HourlyEmployee class and you want to be able to construct these objects out of some XML input too.
<?php
class Employee {
public function __construct($inName) {
$this->name = $inName;
}
public static function constructFromDom($inDom)
{
$name = $inDom->name;
return new Employee($name);
}
private $name;
}
class HourlyEmployee extends Employee {
public function __construct($inName, $inHourlyRate) {
parent::__construct($inName);
$this->hourlyRate = $inHourlyRate;
}
public static function constructFromDom($inDom)
{
// can't call parent::constructFromDom($inDom)
// need to do all the work here again
$name = $inDom->name; // increased coupling
$hourlyRate = $inDom->hourlyrate;
return new EmployeeHourly($name, $hourlyRate);
}
private $hourlyRate;
}
?>
The only solution is to merge the two constructors in one by adding an optional $inDom parameter to every constructor.
david at synatree dot com ¶
16 years ago
When a script is in the process of die()ing, you can't count on the order in which __destruct() will be called.
For a script I have been working on, I wanted to do transparent low-level encryption of any outgoing data. To accomplish this, I used a global singleton class configured like this:
class EncryptedComms
{
private $C;
private $objs = array();
private static $_me;
public static function destroyAfter(&$obj)
{
self::getInstance()->objs[] =& $obj;
/*
Hopefully by forcing a reference to another object to exist
inside this class, the referenced object will need to be destroyed
before garbage collection can occur on this object. This will force
this object's destruct method to be fired AFTER the destructors of
all the objects referenced here.
*/
}
public function __construct($key)
{
$this->C = new SimpleCrypt($key);
ob_start(array($this,'getBuffer'));
}
public static function &getInstance($key=NULL)
{
if(!self::$_me && $key)
self::$_me = new EncryptedComms($key);
else
return self::$_me;
}
public function __destruct()
{
ob_end_flush();
}
public function getBuffer($str)
{
return $this->C->encrypt($str);
}
}
In this example, I tried to register other objects to always be destroyed just before this object. Like this:
class A
{
public function __construct()
{
EncryptedComms::destroyAfter($this);
}
}
One would think that the references to the objects contained in the singleton would be destroyed first, but this is not the case. In fact, this won't work even if you reverse the paradigm and store a reference to EncryptedComms in every object you'd like to be destroyed before it.
In short, when a script die()s, there doesn't seem to be any way to predict the order in which the destructors will fire.
