Enlace estático en tiempo de ejecución

Desde PHP 5.3.0, PHP incorpora una nueva funcionalidad llamada enlace estático en tiempo de ejecución que permite hacer referencias a la clase en uso dentro de un contexto de herencia estática.

De forma más precisa, un enlace estático en tiempo de ejecución para funcionar almacena el nombre de clase de la última llamada que no tenga "propagación". En el caso de las llamadas a métodos estáticos, se trata de la clase a la que se llamó explícitamente (normalmente, la que precede al operador ::); en los casos de llamadas a métodos que no son estáticos, se resolvería a la clase del objeto. Una "llamada con propagación" es una llamada estática que está precedida por self::, parent::, static::, o, si seguimos la jerarquía de clases, forward_static_call(). La función get_called_class() puede utilizarse para obtener un string con el nombre de la clase que realiza la llamada, y static:: revela cuál es su alcance.

Se le ha llamado "enlace estático en tiempo de ejecución" teniendo en cuenta un punto de vista interno. "Enlace en tiempo de ejecución" viene del hecho de que static:: ya resuelve a la clase en la que se definió el método, sino que en su lugar se resolverá utilizando información en tiempo de ejecución debido a que se puede utilizar (entre otras cosas) para las llamadas de métodos estáticos, se le llamó también "enlace estático".

Limitaciones de self::

Las referencias estáticas que hay dentro de la clase en uso, como self:: o __CLASS__, se resuelven empleando el nombre de la clase a la que pertenece la función:

Ejemplo #1 Uso de self::

<?php
class {
    public static function 
who() {
        echo 
__CLASS__;
    }
    public static function 
test() {
        
self::who();
    }
}

class 
extends {
    public static function 
who() {
        echo 
__CLASS__;
    }
}

B::test();
?>

El resultado del ejemplo sería:

A

Uso de Enlace Estático en Tiempo de ejecución

Los enlaces estáticos en tiempo de ejecución tratan de resolver estas limitaciones empleando una palabra clave que haga referencia a la clase que realizó la llamada en tiempo de ejecución. Es decir, una palabra clave que en el ejemplo anterior permita hacer referencia desde test() a B. Se decidió no crear una nueva palabra clave, por lo que en su lugar se ha utilizado la palabra reservada static.

Ejemplo #2 Uso básico de static::

<?php
class {
    public static function 
who() {
        echo 
__CLASS__;
    }
    public static function 
test() {
        static::
who(); // He aquí el enlace estático en tiempo de ejecución
    
}
}

class 
extends {
    public static function 
who() {
        echo 
__CLASS__;
    }
}

B::test();
?>

El resultado del ejemplo sería:

B

Nota:

En contextos no estáticos, la clase que realiza la llamada será la clase del objeto instanciado. Dado que $this-> tratará de invocar métodos privados en su mismo ámbito, el uso de static:: puede provocar diferents resultados. Otra diferencia es que static:: sólo puede hacer referencia a propiedades estáticas.

Ejemplo #3 Uso de static:: en un contexto no estático

<?php
class {
    private function 
foo() {
        echo 
"exito!\n";
    }
    public function 
test() {
        
$this->foo();
        static::
foo();
    }
}

class 
extends {
   
/* foo() se copiará en B, por lo tanto su ámbito seguirá siendo A
    * y la llamada tendrá éxito */
}

class 
extends {
    private function 
foo() {
        
/* se reemplaza el método original; el ámbito del nuevo es ahora C */
    
}
}

$b = new B();
$b->test();
$c = new C();
$c->test();   //falla
?>

El resultado del ejemplo sería:

exito!
exito!
exito!


Fatal error:  Call to private method C::foo() from context 'A' in /tmp/test.php on line 9

Nota:

En una llamada que se resuelva como estática, la resolución de enlaces estáticos en tiempo de ejecución se dentendrá sin propagarse. Por otra parte, las llamadas estáticas que utilicen palabras clave como parent:: o self:: sí propagarán la información.

Ejemplo #4 Llamadas que propagan y que no propagan

<?php
class {
    public static function 
foo() {
        static::
who();
    }

    public static function 
who() {
        echo 
__CLASS__."\n";
    }
}

class 
extends {
    public static function 
test() {
        
A::foo();
        
parent::foo();
        
self::foo();
    }

    public static function 
who() {
        echo 
__CLASS__."\n";
    }
}
class 
extends {
    public static function 
who() {
        echo 
__CLASS__."\n";
    }
}

C::test();
?>

El resultado del ejemplo sería:

A
C
C

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User Contributed Notes 25 notes

up
21
sergei at 2440media dot com
5 years ago
Finally we can implement some ActiveRecord methods:

<?php

class Model
{
    public static function
find()
    {
        echo static::
$name;
    }
}

class
Product extends Model
{
    protected static
$name = 'Product';
}

Product::find();

?>

Output: 'Product'
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1
kx
5 years ago
At least as of PHP 5.3.0a2 there's a function get_called_class(), which returns the class on which the static method is called.

<?php

class a {
  static public function
test() {
    print
get_called_class();
  }
}

class
b extends a {
}

a::test(); // "a"
b::test(); // "b"

?>
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2
Taai
1 year ago
I discovered an interesting thing. The class name string must be accessed directly from "flat" variable. Late static binding code that get's it's variable from array that is passed by class instance, throws an syntax error. Bug?

<?php
class A {

    public
$metadata = array('class' => 'A');

    public static function
numbers()
    {
        return
123;
    }

}

$instance = new A();

// This throws an error
// Parse error: syntax error, unexpected '::' (T_PAAMAYIM_NEKUDOTAYIM)
var_dump( $instance->metadata['class']::numbers() );

// Get the class name and store it in "flat" variable and now it's ok
$class_name = $instance->metadata['class'];
var_dump( $class_name::numbers() );

// Other tests -------------------------------------------

$arr =  array('class' => 'A');

// This works too.
var_dump( $arr['class']::numbers() );
?>
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0
tamilps2 at gmail dot com
1 month ago
I have implemented enum using late static binding.

<?php
interface IEnum {
 
/**
   * Only concrete class should implement this function that should behave as
   * an enum.
   *
   * This method should return the __CLASS__ constant property of that class
   *
   * @return string __CLASS__
   */
 
public static function who();
}

abstract class
Enum {

 
/**
   * The selected value for the enum implementation
   *
   * @var mixed
   */
 
public $value;
 
  public function
__construct($value) {
   
$this->value = $value;
  }
 
 
/**
   * The factory method that creates the corresponding enum class.
   *
   * @param integer $type
   * @return false|\class
   */
 
public static function Factory($type) {
    if (empty(
$type)) {
      return
false;
    }
   
   
// use of late static binding to get the class.
   
$class = static::who();
   
    if (
array_key_exists($type, static::$_enums)) {
      return new
$class($type);
    }
   
    return
false;
  }
 
  public function
getValue() {
    return
$this->value;
  }
 
  public static function
getValues() {
    return
array_keys(static::$_enums);
  }
 
  public function
getString() {
    return static::
$_enums[$this->value];
  }
 
  public function
__toString() {
    return static::
$_enums[$this->value];
  }

}

class
Fruits extends Enum implements IEnum {

      public static
$_enums = array(
           
1 => 'Apple'
           
2 => 'Orange'
           
3 => 'Banana'
     
)

      public static function
who() {
             return
__CLASS__;
      }
}

// Usage

// user input from dropdown menu of fruits list
$input = 3;

$fruit = Fruits::Factory($input);

$fruit->getValue(); // 3
$fruit->getString(); // Banana
?>
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0
steven dot karas+nospam at gmail dot com
3 years ago
This function can be used as a workaround for late static binding in PHP >= 5.1.0. There was another similar version of this function elsewhere, but used eval.

<?php

function & static_var($class, $name)
{
    if (
is_object($class))
    {
       
$class = get_class($class);
    }
    elseif ( !
is_string($class))
    {
        throw new
Exception('Must be given an object or a class name', NULL);
    }
   
   
$class = new ReflectionClass($class);
    return
$class->getStaticPropertyValue($name);
}

?>
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0
iamscrumpyjack
5 years ago
I have been dying to see this issue resolved. I'm very much looking forward to the production release of PHP 5.3...

In my case I have been trying to do the following:

class A {
  function __construct() {
    echo "I was called by " . static::__CLASS__;
  }
}

class B extends A {
  function Foo() {
    echo "I am class " . __CLASS__;
  }
}

$b = new B; // Should echo "I was called by B"
$b->Foo(); // Should echo "I am class B"

At the moment I do the following workaround:

class A {
  function __construct($child) {
    echo "I was called by " . $child;
  }
}

class B extends A {
  function __construct() {
    parent::__construct(__CLASS__);
  }

  function Foo() {
    echo "I am class " . __CLASS__;
  }
}

$b = new B; // Echos "I was called by B"
$b->Foo(); // Echo "I am class B"

As you can see, my current workaround has some overhead and is not as water-tight as the late static binding method.
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0
sebastien at info-conseil dot fr
5 years ago
Here is a small workaround I made for the static inheritance issue. It's not perfect, but it works.

<?php

// BaseClass class will be extended by any class needing static inheritance workaroud
class BaseClass {
   
// Temporarily stores class name for Entry::getStatic() and Entry::setNextStatic()
   
protected static $nextStatic = false;
   
   
// Returns the real name of the class calling the method, not the one in which it was declared.
   
protected static function getStatic() {
       
// If already stored
       
if (self::$nextStatic) {
           
// Clean and return
           
$class = self::$nextStatic;
           
self::$nextStatic = false;
            return
$class;
        }
       
       
// Init
       
$backTrace = debug_backtrace();
       
$class = false;
       
       
// Walk through
       
for ($i=0; $i<count($backTrace); $i++) {
           
// If a class is defined
           
if (isset($backTrace[$i]['class'])) {
               
// Check if it is not a basic class
               
if (!in_array($backTrace[$i]['class'], array('BaseClass', 'GenericClass'))) {
                    return
$backTrace[$i]['class'];
                } else {
                   
$class = $backTrace[$i]['class'];
                }
            } else {
               
// Returns last known class
               
return $class;
            }
        }
       
       
// Default
       
return $class;
    }
   
   
// If a static method is called within global env, the previous method won't work, so we need to tell BaseClass which
   
public static function setNextStatic($class) {
       
// Save value
       
self::$nextStatic = $class;
    }
}

// Generic class declaring various static methods
class GenericClass extends BaseClass {
    public static
$name = 'Generic';
   
    public function
getName() {
       
$static = get_class_vars(get_class($this));
        return
$static['name'];
    }
   
    public static function
basicClassName() {
        return
self::$name;
    }
   
    public static function
staticClassName() {
       
// Get real name
       
$staticName = self::getStatic();
       
       
// Return final class name
       
$static = get_class_vars($staticName);
        return
$static['name'];
    }
}

// Final class
class SomeClass extends GenericClass {
    public static
$name = 'Some';
   
    public static function
returnClassNameWith($string) {
        return
$string.' : '.self::staticClassName();
    }
}

// Instance call

// Will print 'Some'
$a = new SomeClass();
echo
'Name of $a : '.$a->getName().'<br />';

// Static calls

// Will print 'Generic'
echo 'Basic call to SomeClass::$name : '.SomeClass::basicClassName().'<br />';

// Will print 'Generic'
echo 'Global call to SomeClass::$name : '.SomeClass::staticClassName().'<br />';

// Will print 'Some'
BaseClass::setNextStatic('SomeClass');
echo
'Global call to SomeClass::$name with pre-set : '.SomeClass::staticClassName().'<br />';

// Will print 'Some'
echo 'Internal call to SomeClass::$name : '.SomeClass::returnClassNameWith('This is a ').'<br />';

?>

There are two issues with this workaround :
- if you call a static method from global env, you need to declare the name of the class BEFORE calling the method, otherwise the workaround won't work (see 3rd and 4th examples). But I assume good programming makes few calls to static methods from global scope, so this shouldn't be long to fix if you use it.
- the workaround fails to access to private or protected static vars, as it uses get_class_vars(). If you find any better solution, let us know.

With Php 5.3.0, upgrading will be easy : just delete the methods from the basic class, and search/replace any call to getStatic() and setNextStatic() by static:: - or one could use a selector on PHP_VERSION value to include either the BaseClass file with workaround or a BaseClass file using static::
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0
Anonymous
5 years ago
Trying to recreate an inheritable static part for an object through a singleton pattern.

<?php
/**
 * "Inheritable static" for PHP < 5.3
 * << Library/Inheritable.php >>
 */

abstract class Inheritable_Static extends Singleton
{
}

abstract class
Inheritable
{
    public static function
getStatic($className)
    {
       
// Use an abstract Singleton
       
return Singleton::getInstance($className . '_Static') ;
    }
   
    public function
goStatic()
    {
        return
self::getStatic(get_class($this)) ;
    }
}

/**
 * Abstract
 * << Library/SayIt/Abstract.php >>
 */

abstract class SayIt_Abstract_Static extends Inheritable_Static
{
    public
$format ;
}

abstract class
SayIt_Abstract extends Inheritable
{
    protected
$_name ;
   
    public function
__construct($name)
    {
       
$this->_name = $name ;
    }
   
    final public function
sayIt()
    {
        echo
sprintf($this->goStatic()->format, $this->_name) . "\n" ;
    }
   
}

/**
 * Concrete
 * << Library/SayIt/Hello.php >>
 */

class SayIt_Hello_Static extends SayIt_Abstract_Static
{
}

class
SayIt_Hello extends SayIt_Abstract
{
    public static function
getStatic() { return parent::getStatic(__CLASS__) ; }
}

/**
 * Test
 */

SayIt_Hello::getStatic()->format = 'Hello %s' ;

$w = new SayIt_Hello('World') ;
$j = new SayIt_Hello('Joe') ;

echo
$w->sayIt() ; // Hello World
echo $j->sayIt() ; // Hello Joe
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0
Andrea Giammarchi
5 years ago
About static parameters, these work as expected.
<?php
class A {
    protected static
$__CLASS__ = __CLASS__;
    public static function
constructor(){
        return  static::
$__CLASS__;
    }
}

class
B extends A {
    protected static
$__CLASS__ = __CLASS__;
}

echo   
B::constructor(); // B
?>
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0
martinpauly [at] google mail [dot] com
5 years ago
will this work for variables as well?

it would be great, if the following worked:

<?php
class A {
protected static
$table = "table";
public static function
connect(){
    
//do some stuff here
    
echo static::$table;
     return static::
getInstance(); //function getInstance() now can return classes A or B depending on the context it was called
}
...
}

class
B extends A {
protected static
$table = "subtable";
...
}

$table = B::connect(); //hopefully the output will be: subtable
?>
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0
deadimp at gmail dot com
5 years ago
I think this will be pretty helpful too.
My question is, can just 'static' by itself resolve to the late static class?
I ask this because it could help in making new instances of the derived class, from a base class, by calling a derived class's static method instead of having to create a new instance of the derived class - or explicitly defining a 'getClass' method for each derived class.
Example:
<?php
//There isn't really any purpose for this example I posted
//Just a random implementation
class Base {
    static function
useful() {
       
//Create a list of instances of the derived class
       
$list=array();
        for (
$i=0;$i<10;$i++) $list[]=new static(); //Here's the point in question
       
return $list;
    }
}
class
Derived extends Base {
    static function
somethingElse() {
       
//...
       
$list=static::useful();
    }
}
?>
I'm not sure what kind of lexical / whatever-it's-called problems this would make with parsing. I don't think it could really collide with any contexts where you would use static otherwise - variable / method declaration.

Even more so, is there a way to get the class's name to which the keywords 'self', 'parent', or 'static' refer?
Example:
<?php
class Base {
    static function
stuff() {
        echo
"Self: ".get_class(self);
        echo
"Parent: ".get_class(parent);
        echo
"Derived: ".get_class(static);
    }
}
class
Derived extends Base {
    static function
stuff() {
        static::
stuff();
    }
}
?>

I don't think there should be a massive bloat in the PHP core to support all of this, but it would be nice to take advantage of the dynamic nature of PHP.

And yet another side note:
If you're in the instance-level scope in a method of a base, and you want to get a top-level static, here's an ugly workaround (from Thacmus /lib/core.php - see SVN repo):
<?php
//Get reference [?] to static from class
    //$class - Class name OR object (uses get_class())
    //$var - Not gonna say
function& get_static($class,$var) { //'static_get'?
   
if (!is_string($class)) $class=get_class($class);
    if (!@
property_exists($class,$var)) {
       
trigger_error("Static property does not exist: $class::\$$var");
       
//debug_callstack(); //This is just a wrapper for debug_backtrace() for HTML
       
return null;
    }
   
//Store a reference so that the base data can be referred to
        //The code [[ return eval('return &'.$class.'::$'.$var.';') ]] does not work - can not return references...
        //To establish the reference, use [[ $ref=&get_static(...) ]]
   
eval('$temp=&'.$class.'::$'.$var.';'); //using
   
return $temp;
}
?>
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0
tyler AT canfone [dot] COM
5 years ago
@ php at mikebird

You can pass arguments to your constructor through your getInstance method, assuming you are running php5.

        public static function getInstance($params = null) {
            if (self::$objInstance == null) {
                $strClass = static::getClass();
                self::$objInstance = new $strClass($params);
            }
            return self::$objInstance;
        }

This would pass the params to your constructor. Love for php.
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0
php at mikebird dot co dot uk
5 years ago
This should make life easier and neater if you have a project with a lot of singleton classes e.g.

<?php

   
class Singleton {
       
        public static
$objInstance;
   
        public static function &
getInstance() {
            if (
self::$objInstance == null) {
               
$strClass = static::getClass();
               
self::$objInstance = new $strClass;
            }
            return
self::$objInstance;
        }
       
        public static function
getClass() {
            return
__CLASS__;
        }
   
    }

    class
Foo extends Singleton {
       
        public
$intBar;
       
        public function
__construct() {
           
$this->intBar = 1;
        }
       
        public static function
getClass() {
            return
__CLASS__;
        }
       
    }
   
   
   
$objFooTwo = Foo::getInstance();
   
$objFooTwo->intBar = 2;
   
   
$objFooOne = Foo::getInstance();
   
    if (
$objFooOne->intBar == $objFooTwo->intBar) {
        echo
'it is a singleton';
    } else {
        echo
'it is not a singleton';
    }

?>

The above will output 'it is a singleton'. The obvious downfall to this method is not being able to give arguments to the constructor.
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0
max at mastershrimp dot com
6 years ago
If you are using PHP < 5.3.0 you might be interested in the following workaround for late static binding: http://de2.php.net/manual/de/function.get-class.php#77698
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-1
jrfish dot x at gmail dot com
3 years ago
also works the same way with static variables and constants
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-1
jrfish dot x at gmail dot com
3 years ago
consider this:

<?php
class A
{

 
// some stuff....

   
public static function getInstance()
    {
        return new
self();
    }

}

class
B extends A
{
 
//stuff...
}

$obj = B::getInstance();

//versus

class A
{

 
// some stuff....

   
public static function getInstance()
    {
        return new static();
    }

}

class
B extends A
{
 
//stuff...
}

$obj = B::getInstance();
?>

also works the same way with static variables and constants
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-1
adam dot prall at thinkingman dot com
3 years ago
Just a quick reminder to always check your syntax. While I love LSB, I thought it wasn't working:

static::$sKey = not set

…until I realized that I’d completely forgotten to make it a variable variable:

$sKey = 'testStaticClassVarNameThatExistsInThisClassesScope';

static::$$sKey = is set

…of course this applies anywhere in PHP, but because of the (current) newness late static bindings, I’ve seen lots of code with this particular snafu in it from others.
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-1
joost dot t dot hart at planet dot nl
4 years ago
PHP5.3 unavailable, yet in the need for 'static', I did the following.

Any objections? Personally I hate using the the eval() statement...

<?php

class mother
{
    function
setStatic( $prop, $val ) {
       
// After this, self:: refers to mother, yet next $class refers to...
        //
       
$class = get_class( $this );
        eval(
"$class::\$$prop = \$$val;" );
    }
}

class
child extends mother
{
    protected static
$sProp;

    function
writer( $value ) {
       
parent::setStatic( 'sProp', $value );
    }
    function
reader()
    {
        return
self::$sProp;
    }
}

$c = new child();
$c->writer( 3 );
echo
$c->reader(); // 3

?>
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-1
tom
4 years ago
Something you may find useful for passive code-testing:

<?php
class BaseClass {
  function
__get($id) {
    throw new
Exception("Trying to access undefined property '$id'.");
  }
  function
__set($id) {
    throw new
Exception("Trying to access undefined property '$id'.");
  }
}

class
MyClass extends BaseClass {
// my implementation
}
?>

Using these magic function as described above will help you to find classes that try to access an undefined (and undocumented) class-member. In most cases: this is an error based on misspelled member names.
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-1
jakub dot lopuszanski at nasza-klasa dot pl
3 years ago
Suprisingly consts are also lazy bound even though you use self instead of static:
<?php
class A{
  const
X=1;
  const
Y=self::X;
}
class
B extends A{
  const
X=1.0;
}
var_dump(B::Y); // float(1.0)
?>
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-1
gern_ at hotmail dot com
5 years ago
get_called_class for PHP < 5.3

<?php
/**
 * Return called class name
 *
 * @author Michael Grenier
 * @param int $i_level optional
 * @return string
 */
function get_called_class ($i_level = 1)
{
   
$a_debug = debug_backtrace();
   
$a_called = array();
   
$a_called_function = $a_debug[$i_level]['function'];
    for (
$i = 1, $n = sizeof($a_debug); $i < $n; $i++)
    {
        if (
in_array($a_debug[$i]['function'], array('eval')) ||
           
strpos($a_debug[$i]['function'], 'eval()') !== false)
            continue;
        if (
in_array($a_debug[$i]['function'], array('__call', '__callStatic')))
           
$a_called_function = $a_debug[$i]['args'][0];
        if (
$a_debug[$i]['function'] == $a_called_function)
           
$a_called = $a_debug[$i];
    }
    if (isset(
$a_called['object']) && isset($a_called['class']))
        return (string)
$a_called['class'];
   
$i_line = (int)$a_called['line'] - 1;
   
$a_lines = explode("\n", file_get_contents($a_called['file']));
   
preg_match("#([a-zA-Z0-9_]+){$a_called['type']}
               
{$a_called['function']}( )*\(#", $a_lines[$i_line], $a_match);
    unset(
$a_debug, $a_called, $a_called_function, $i_line, $a_lines);
    if (
sizeof($a_match) > 0)
       
$s_class = (string)trim($a_match[1]);
    else
       
$s_class = (string)$a_called['class'];
    if (
$s_class == 'self')
        return
get_called_class($i_level + 2);
    return
$s_class;
}
?>
up
-1
mhh1422 at hotmail dot com
3 months ago
For abstract classes with static factory method, you can use the static keyword instead of self like the following:
<?php

abstract class A{
   
    static function
create(){

       
//return new self();  //Fatal error: Cannot instantiate abstract class A

       
return new static(); //this is the correct way

   
}
   
}

class
B extends A{
}

$obj=B::create();
var_dump($obj);

?>
up
-2
Anonymous
3 years ago
THIS WORKED GREAT FOR ME:

<?php
abstract class ParentClass
{
    static function
parent_method()
    {
       
$child_class_str = self::get_child_class();
        eval(
"\$r = ".$child_class_str."::abstract_static();");
        return
$r;
    }
// CHILD MUST OVERRIDE TO PUT ITSELF INTO TRACE

   
protected abstract static function abstract_static();

    private static function
get_child_class()
    {
       
$backtrace = debug_backtrace();
       
$num = count($backtrace);
        for(
$i = 0; $i < $num; $i++)
        {
            if(
$backtrace[$i]["class"] !== __CLASS__)
                return
$backtrace[$i]["class"];
        }
        return
null;
    }
}

class
ChildClass extends ParentClass
{
    static function
parent_method(){ return parent::parent_method(); }

    protected static function
abstract_static()
    {
        return
__METHOD__."()";
    }
// From ParentClass
}

print
"The call was: ". ChildClass::parent_method();
?>
up
-3
kenneth at kennethjorgensen dot com
5 years ago
Simple basic class which uses to get_called_class() to create singleton instances. A previous post by php at mikebird dot co dot uk explain how to do this, but the extended static variables require you to define them in child classes before they work.

<?php

abstract class Singleton {
    private static
$instances = array();
   
    public function
__construct() {
       
$class = get_called_class();
        if (
array_key_exists($class, self::$instances))
           
trigger_error("Tried to construct  a second instance of class \"$class\"", E_USER_WARNING);
    }
   
    public static function
getInstance() {
       
$class = get_called_class();
        if (
array_key_exists($class, self::$instances) === false)
           
self::$instances[$class] = new $class();
        return
self::$instances[$class];
    }
}

class
A extends Singleton {
}

class
B extends Singleton {
}

$a1 = A::getInstance();
$a2 = A::getInstance();
$b1 = B::getInstance();
$b2 = B::getInstance();

if (
get_class($a1) == "A" &&
   
get_class($a2) == "A" &&
   
get_class($b1) == "B" &&
   
get_class($b2) == "B" &&
   
$a1 === $a2 &&
   
$b1 === $b2)
    echo
"All good\n";
else
    echo
"FAIL!\n";

?>

You probably noticed the use of self:: rather than static::, this is because we want the static variable to be private, and using static:: will not allow us to do that.
up
-3
tfn dot yldrm at hotmail dot com
3 years ago
example for static binding on 5.2 and real enumaration
<?php
   
/**
    * Static Binding On PHP 5.2
    * @author Tufan Baris YILDIRIM
    * @since 26.10.2010
    */
   
abstract class EnumBase
   
{  
        protected
$num = 0;
        public
$toString;
        public
$toInt;

        public function
__construct($enumKeyOrVal)
        {  

            unset(
$this->toString,$this->toInt);

           
$enums = $this->enums();

            if(
            empty(
$enumKeyOrVal)
            ||
            !(isset(
$enums[$this->num = $enumKeyOrVal])
            ||
            (
$this->num = array_search($enumKeyOrVal,$enums)) !== false)
            )
               
$this->num = 0;

           
/**
            *  5.3 Version
            */
            /*
            *  if(
            empty($enumKeyOrVal)
            ||
            !(isset(static::$enums[$this->num = $enumKeyOrVal])
            ||
            ($this->num = array_search($enumKeyOrVal,static::$enums)) !== false)
            )
            $this->num = 0;
            */
       
}

       
#5.3 e geçilirse gerek kalmaz.
       
public function vars()
        {
            return
get_class_vars(get_class($this));
        }

        public function
enums()
        {
           
$vars = $this->vars();
            return
$vars['enums'];
        }

        public function
__get($property)
        {
            if(
method_exists($this,'__'.$property))
                return
$this->{'__'.$property}();
            else
                return
$this->__toString();
        }                                  

        public function
__toInt()
        {
            return
$this->num;
        }

        public function
__toString()
        {

           
$enums = $this->enums();

            if(isset(
$enums[$this->num]))
            {
                return
$enums[$this->num];
            }
            else
            {
                return
$enums[0];
            }

           
/**
            * 5.3 Version
            */

            /*
            if(isset(static::$enums[$this->num]))
            {
            return static::$enums[$this->num];
            }
            else
            {
            return static::$enums[0];
            }
            */
       
}
    }

    class
Positions extends EnumBase
   
{
        public static
$enums = array(
       
0 => 'Bilinmiyor',
       
1 => 'Kale',
       
2 => 'Defans',
       
3 => 'Orta Saha',
       
4 => 'Forvet'
       
); 
    }

    
   
$a = new Positions('Orta Saha');
   
$b = new Positions(4);

   
$c = (string)$a; // Orta Saha
   
$d = (string)$b; // Forvet
?>
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