Конструкторы и деструкторы

Constructor

PHP 5 позволяет объявлять методы-конструкторы. Классы, в которых объявлен метод-констуктор, будут вызывать этот метод при каждом создании нового объекта, так что это может оказаться полезным, чтобы, например, инициализировать какое-либо состояние объекта перед его использованием.

Замечание: Конструкторы в классах-родителях не вызываются автоматически. Чтобы вызвать конструктор, объявленный в родительском классе, следует обратиться к методу parent::__construct().

Пример #1 Использование унифицированных конструкторов

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

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

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

Если PHP 5 не может обнаружить объявленный метод __construct(), вызов конструктора произойдет по прежней схеме, через обращение к методу, имя которого соответствует имени класса. Может возникнуть только одна проблема совместимости старого кода, если в нём присутствуют классы с методами __construct().

Деструкторы

PHP 5 предоставляет концепцию деструкторов, сходную с теми, что применяются в других ОО языках, таких, как Java: когда освобождается последняя ссылка на объект, перед высвобождением памяти, занимаемой этим объектом, вызывается метод __destruct(), не принимающий параметров.

Пример #2 Пример использования деструктора

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

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

$obj = new MyDestructableClass();
?>

Как и в случае с конструкторами, деструкторы, объявленные в родительском классе, не будут вызваны автоматически. Для вызова деструктора, объявленном в классе-родителе, следует обратиться к методу parent::__destruct().

Коментарии

Автор:
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.
2006-07-10 17:18:49
http://php5.kiev.ua/manual/ru/language.oop5.decon.html
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
2007-07-27 03:42:56
http://php5.kiev.ua/manual/ru/language.oop5.decon.html
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.
2007-12-29 15:26:28
http://php5.kiev.ua/manual/ru/language.oop5.decon.html
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.
2008-04-16 21:13:19
http://php5.kiev.ua/manual/ru/language.oop5.decon.html
Автор:
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!
2008-10-17 19:35:15
http://php5.kiev.ua/manual/ru/language.oop5.decon.html
Автор:
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 ;)
2010-01-09 18:32:13
http://php5.kiev.ua/manual/ru/language.oop5.decon.html
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->namePHP_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: features.gc
// 

// 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.
2011-08-12 07:17:37
http://php5.kiev.ua/manual/ru/language.oop5.decon.html
Автор:
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.
2012-05-09 16:57:02
http://php5.kiev.ua/manual/ru/language.oop5.decon.html
<?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.
2013-08-23 00:06:20
http://php5.kiev.ua/manual/ru/language.oop5.decon.html
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.
2017-08-14 10:53:28
http://php5.kiev.ua/manual/ru/language.oop5.decon.html
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
2020-01-16 09:58:03
http://php5.kiev.ua/manual/ru/language.oop5.decon.html
/**
 * 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();
2021-02-27 12:07:24
http://php5.kiev.ua/manual/ru/language.oop5.decon.html
*<Double post> I can't edit my previous note to elaborate on modifiers. Please excuse me.*

If both parent and child classes have a method with the same name defined, and it is called in parent's constructor, using `parent::__construct()` will call the method in the child.

<?php

class {
    public function 
__construct() {
       
$this->method();
    }
    public function 
method() {
        echo 
'A' PHP_EOL;
    }
}
class 
extends {
    public function 
__construct() {
       
parent::__construct();
    }
}
class 
extends {
    public function 
__construct() {
       
parent::__construct();
    }
    public function 
method() {
        echo 
'C' PHP_EOL;
    }
}
$b = new B// A
$c = new C// C

?>

In this example both A::method and C::method are public.

You may change A::method to protected, and C::method to protected or public and it will still work the same.

If however you set A::method as private, it doesn't matter whether C::method is private, protected or public. Both $b and $c will echo 'A'.
2022-03-10 18:56:42
http://php5.kiev.ua/manual/ru/language.oop5.decon.html
Please note that constructor argument promotion is kind of half-baked (at least as of 8.1 and it does not look to be changed in 8.2) and you are not allowed to reuse promoted argument with other promoted arguments. For example having "old style" constructor:

<?php
public function __construct(protected string $val, protected Foo $foo null) {
   
$this->val $val;
   
$this->foo $foo ?? new Foo($val);
}
?>

you will not be able to use argument promotion like this:

<?php
public function __construct(protected string $val, protected Foo $foo = new Foo($val)) {}
?>

nor

<?php
public function __construct(protected string $val, protected Foo $foo = new Foo($this->val)) {}
?>

as in both cases you will face "PHP Fatal error:  Constant expression contains invalid operations".
2022-08-16 12:04:05
http://php5.kiev.ua/manual/ru/language.oop5.decon.html
Автор:
There are other advantages to using static factory methods to wrap object construction instead of bare constructor calls.

As well as allowing for different methods to use in different scenarios, with more relevant names both for the methods and the parameters and without the constructor having to handle different sets of arguments of different types:

* You can do all your input validation before attempting to construct the object.
* The object itself can bypass that input validation when constructing new instances of its own class, since you can ensure that it knows what it's doing.
* With input validation/preprocessing moved to the factory methods, the constructor itself can often be reduced to "set these properties to these arguments", meaning the constructor promotion syntax becomes more useful.
* Having been hidden away from users, the constructor's signature can be a bit uglier without becoming a pain for them. Heh.
* Static methods can be lifted and passed around as first class closures, to be called in the normal fashion wherever functions can be called, without the special "new" syntax.
* The factory method need not return a new instance of that exact class. It could return a pre-existing instance that would do the same job as the new one would (especially useful in the case of immutable "value type" objects by reducing duplication); or a simpler or more specific subclass to do the job with less overhead than a more generic instance of the original class. Returning a subclass means LSP still holds.
2023-08-29 06:11:19
http://php5.kiev.ua/manual/ru/language.oop5.decon.html

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