Late Static Bindings

As of PHP 5.3.0, PHP implements a feature called late static bindings which can be used to reference the called class in a context of static inheritance.

More precisely, late static bindings work by storing the class named in the last "non-forwarding call". In case of static method calls, this is the class explicitly named (usually the one on the left of the :: operator); in case of non static method calls, it is the class of the object. A "forwarding call" is a static one that is introduced by self::, parent::, static::, or, if going up in the class hierarchy, forward_static_call(). The function get_called_class() can be used to retrieve a string with the name of the called class and static:: introduces its scope.

This feature was named "late static bindings" with an internal perspective in mind. "Late binding" comes from the fact that static:: will not be resolved using the class where the method is defined but it will rather be computed using runtime information. It was also called a "static binding" as it can be used for (but is not limited to) static method calls.

Limitations of self::

Static references to the current class like self:: or __CLASS__ are resolved using the class in which the function belongs, as in where it was defined:

Example #1 self:: usage

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

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

B::test();
?>

The above example will output:

A

Late Static Bindings' usage

Late static bindings tries to solve that limitation by introducing a keyword that references the class that was initially called at runtime. Basically, a keyword that would allow you to reference B from test() in the previous example. It was decided not to introduce a new keyword but rather use static that was already reserved.

Example #2 static:: simple usage

<?php
class {
    public static function 
who() {
        echo 
__CLASS__;
    }
    public static function 
test() {
        static::
who(); // Here comes Late Static Bindings
    
}
}

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

B::test();
?>

The above example will output:

B

Note:

In non-static contexts, the called class will be the class of the object instance. Since $this-> will try to call private methods from the same scope, using static:: may give different results. Another difference is that static:: can only refer to static properties.

Example #3 static:: usage in a non-static context

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

class 
extends {
   
/* foo() will be copied to B, hence its scope will still be A and
    * the call be successful */
}

class 
extends {
    private function 
foo() {
        
/* original method is replaced; the scope of the new one is C */
    
}
}

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

The above example will output:

success!
success!
success!

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

Note:

Late static bindings' resolution will stop at a fully resolved static call with no fallback. On the other hand, static calls using keywords like parent:: or self:: will forward the calling information.

Example #4 Forwarding and non-forwarding calls

<?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();
?>

The above example will output:

A
C
C

Коментарии

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
2008-04-10 18:24:31
http://php5.kiev.ua/manual/ru/language.oop5.late-static-bindings.html
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.
2008-04-23 11:39:48
http://php5.kiev.ua/manual/ru/language.oop5.late-static-bindings.html
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'
2008-05-28 16:22:38
http://php5.kiev.ua/manual/ru/language.oop5.late-static-bindings.html
@ 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.
2008-06-05 01:48:34
http://php5.kiev.ua/manual/ru/language.oop5.late-static-bindings.html
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;
}
?>
2008-06-05 13:39:32
http://php5.kiev.ua/manual/ru/language.oop5.late-static-bindings.html
will this work for variables as well?

it would be great, if the following worked:

<?php
class {
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 
extends {
protected static 
$table "subtable";
...
}

$table B::connect(); //hopefully the output will be: subtable
?>
2008-06-18 08:54:09
http://php5.kiev.ua/manual/ru/language.oop5.late-static-bindings.html
Автор:
About static parameters, these work as expected.
<?php
class {
    protected static 
$__CLASS__ __CLASS__;
    public static function 
constructor(){
        return  static::
$__CLASS__;
    }
}

class 
extends {
    protected static 
$__CLASS__ __CLASS__;
}

echo   
B::constructor(); // B
?>
2008-06-21 16:06:09
http://php5.kiev.ua/manual/ru/language.oop5.late-static-bindings.html
Автор:
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
2008-07-12 15:49:11
http://php5.kiev.ua/manual/ru/language.oop5.late-static-bindings.html
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::
2008-07-17 10:26:29
http://php5.kiev.ua/manual/ru/language.oop5.late-static-bindings.html
Автор:
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.
2008-09-07 12:01:41
http://php5.kiev.ua/manual/ru/language.oop5.late-static-bindings.html
Автор:
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 {
  static public function 
test() {
    print 
get_called_class();
  }
}

class 
extends {
}

a::test(); // "a"
b::test(); // "b"

?>
2008-09-14 12:39:32
http://php5.kiev.ua/manual/ru/language.oop5.late-static-bindings.html
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;
}
?>
2008-09-18 10:51:29
http://php5.kiev.ua/manual/ru/language.oop5.late-static-bindings.html
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() {
       
$class get_called_class();
        if (
array_key_exists($classself::$instances))
           
trigger_error("Tried to construct  a second instance of class \"$class\""E_USER_WARNING);
    }
   
    public static function 
getInstance() {
       
$class get_called_class();
        if (
array_key_exists($classself::$instances) === false)
           
self::$instances[$class] = new $class();
        return 
self::$instances[$class];
    }
}

class 
extends Singleton {
}

class 
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.
2009-03-30 05:19:00
http://php5.kiev.ua/manual/ru/language.oop5.late-static-bindings.html
Автор:
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.
2009-07-03 09:28:57
http://php5.kiev.ua/manual/ru/language.oop5.late-static-bindings.html
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);
echo 
$c->reader(); // 3

?>
2009-08-21 09:34:40
http://php5.kiev.ua/manual/ru/language.oop5.late-static-bindings.html
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.
2010-06-11 12:51:23
http://php5.kiev.ua/manual/ru/language.oop5.late-static-bindings.html
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);
}

?>
2010-09-27 17:38:48
http://php5.kiev.ua/manual/ru/language.oop5.late-static-bindings.html
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(
       
=> 'Bilinmiyor',
       
=> 'Kale',
       
=> 'Defans',
       
=> 'Orta Saha',
       
=> 'Forvet'
       
); 
    }

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

   
$c = (string)$a// Orta Saha
   
$d = (string)$b// Forvet
?>
2010-10-26 15:30:45
http://php5.kiev.ua/manual/ru/language.oop5.late-static-bindings.html
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 
extends A{
  const 
X=1.0;
}
var_dump(B::Y); // float(1.0)
?>
2010-11-08 12:12:48
http://php5.kiev.ua/manual/ru/language.oop5.late-static-bindings.html
Автор:
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();
?>
2010-11-24 11:22:08
http://php5.kiev.ua/manual/ru/language.oop5.late-static-bindings.html
consider this:

<?php
class A
{

 
// some stuff....

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

}

class 
extends A
{
 
//stuff...
}

$obj B::getInstance();

//versus

class A
{

 
// some stuff....

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

}

class 
extends A
{
 
//stuff...
}

$obj B::getInstance();
?>

also works the same way with static variables and constants
2010-12-09 06:01:59
http://php5.kiev.ua/manual/ru/language.oop5.late-static-bindings.html
also works the same way with static variables and constants
2010-12-09 06:05:04
http://php5.kiev.ua/manual/ru/language.oop5.late-static-bindings.html
Автор:
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 {

    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() );
?>
2012-08-21 13:36:54
http://php5.kiev.ua/manual/ru/language.oop5.late-static-bindings.html
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 
extends A{
}

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

?>
2013-12-29 13:58:15
http://php5.kiev.ua/manual/ru/language.oop5.late-static-bindings.html
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(
           
=> 'Apple'
           
=> 'Orange'
           
=> '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
?>
2014-03-20 07:42:26
http://php5.kiev.ua/manual/ru/language.oop5.late-static-bindings.html
static::class and self::class can be used to get current class name, 
work under 5.5 and 5.6
failed in 5.3.

<?php
class a
    function 
d() {
        echo 
"=== self::class ===\n";
       
var_dump(self::class);
        echo 
"=== static::class ===\n";
       
var_dump(static::class);
    }
}
class 
extends a{}
class 
extends b{}

a::d(); 
b::d();
c::d();

/*
Output: 

=== self::class ===
string(1) "a"
=== static::class ===
string(1) "a"
=== self::class ===
string(1) "a"
=== static::class ===
string(1) "b"
=== self::class ===
string(1) "a"
=== static::class ===
string(1) "c"

*/
2015-08-31 07:01:56
http://php5.kiev.ua/manual/ru/language.oop5.late-static-bindings.html
Автор:
<?php

class 
{
   
}

class 
extends 
{
    public static function 
foo () {
        echo 
'new self: ';
       
var_dump(new self());
        echo 
'<br>new parent: ';
       
var_dump(new parent());
        echo 
'<br>new static: ';
       
var_dump(new static());
    }
}

class 
extends 
{
   
}

c::foo();
===========================
output:
//new self: object(B)#1 (0) { }
//new parent: object(A)#1 (0) { }
//new static: object(C)#1 (0) { }
2018-04-26 12:26:52
http://php5.kiev.ua/manual/ru/language.oop5.late-static-bindings.html
Автор:
In the above example (#3) in order to make it work, you can change the child's method from 'private' to 'protected' (or public) and it will be called through 'static'.

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

class 
extends {
   
/* foo() will be copied to B, hence its scope will still be A and
    * the call be successful */
}

class 
extends {
    protected function 
foo() { //note the change here
         
echo 'hello world!';
    }
}

$b = new B();
$b->test();
$c = new C();
$c->test();   // 'success' 'hello world'
?>
2021-09-04 14:07:34
http://php5.kiev.ua/manual/ru/language.oop5.late-static-bindings.html
Автор:
class P_Class {
    public static $val = "Parent";
    public static function setVal($val){
        static::$val = $val;
    }
    public static function getVal(){
        return static::$val;
    }
}

class C_Class extends P_Class{}

C_Class::setVal("Child");
var_dump(C_Class::getVal());
var_dump(P_Class::getVal());

Output:
string(5) "Child"
string(5) "Child"
2022-02-19 11:02:05
http://php5.kiev.ua/manual/ru/language.oop5.late-static-bindings.html
Simplest way to understand is to run this script:

<?php
class ParentClass
{
    static 
$A 'ParentVariable';

    static function 
parentCall()
    {
        echo 
get_called_class() . ', self: ' self::$A "\n";
        echo 
get_called_class() . ', static: ' . static::$A "\n";
        echo 
"---\n";
    }
}

class 
ChildClass extends ParentClass
{
    static 
$A 'ChildVariable';

    static function 
childCall()
    {
        echo 
get_called_class() . ', self: ' self::$A "\n";
        echo 
get_called_class() . ', static: ' . static::$A "\n";
        echo 
get_called_class() . ', parent: ' parent::$A "\n";
        echo 
"---\n";
    }
}

echo 
"Late Static Bindings:\n";
ParentClass::parentCall();
ChildClass::parentCall();
ChildClass::childCall();
?>

----
Output:

Late Static Bindings:
ParentClass, self: ParentVariable
ParentClass, static: ParentVariable
---
ChildClass, self: ParentVariable
ChildClass, static: ChildVariable
---
ChildClass, self: ChildVariable
ChildClass, static: ChildVariable
ChildClass, parent: ParentVariable
2022-03-27 22:05:35
http://php5.kiev.ua/manual/ru/language.oop5.late-static-bindings.html
You must be careful when getting static property of extended class from parent class, in example below you can see that using property_exists (method getA2) instead of isset with static keyword (method getA1) to check if the static property exist gives much more intuitive result:

<?php
class Foo
{
    public static 
string $A;

    public static function 
init() {
        return static::class;
    }

    public static function 
getA1() {
        if (!isset(static::
$A)) {
            static::
$A = static::class;
        }
        return static::
$A;
    }
   
    public static function 
getA2() {
        if (
property_exists(static::class, 'A')) {
            static::
$A = static::class;
        }
        return static::
$A;
    }
}
class 
Bar extends Foo {}

$foo = new Foo();
echo 
$foo->getA1();
echo 
$foo->getA2();
echo 
$foo->getA1();

$bar = new Bar();
echo 
$bar->getA1();
echo 
$bar->getA2();
echo 
$bar->getA1();
?>

Output:
Foo
Foo
Foo

Foo
Bar
Bar

Notice how $bar->getA1() returns "Foo" instead of "Bar" that many people would expect to see.
2022-07-29 10:14:48
http://php5.kiev.ua/manual/ru/language.oop5.late-static-bindings.html
Example of setting up static property in child class from parent only if it isn't already defined, many people would expect that output will be "Foo Bar" but instead we get "Foo Foo":

<?php
class Foo
{
    public static 
string $A;

    public static function 
init() {
        return 
"Foo";
    }
    public static function 
get() {
        if (!isset(static::
$A)) {
            static::
$A = static::init();
        }
        return static::
$A;
    }
}

class 
Bar extends Foo {
    public static function 
init() {
        return 
"Bar";
    }
}

$foo = new Foo();
$bar = new Bar();

echo 
$foo->get();
echo 
$bar->get();
?>

Output:
Foo
Foo
2022-07-29 10:38:25
http://php5.kiev.ua/manual/ru/language.oop5.late-static-bindings.html
Автор:
Word of caution static::class doesn't always work as you might expect
<?php
namespace NameSpace;

class Class
{
    static function 
getClass()
    {
         return static::class;
    }
}

Class::
getClass()
?>
may return \NameSpace\Class or Class depending on context
2022-10-25 14:52:01
http://php5.kiev.ua/manual/ru/language.oop5.late-static-bindings.html

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