International PHP Conference Berlin 2025

Late Static Bindings (Résolution statique à la volée)

PHP implémente une fonctionnalité appelée late static binding, en français la résolution statique à la volée, qui peut être utilisée pour référencer la classe appelée dans un contexte d'héritage statique.

Plus précisément, les résolutions statiques à la volée fonctionnent en enregistrant le nom de la classe dans le dernier "appel non transmis". Dans le cas des appels de méthodes statiques, il s'agit de la classe explicitement nommée (généralement, celle à gauche de l'opérateur ::) ; dans le cas de méthodes non statiques, il s'agit de la classe de l'objet. Un "appel transmis" est un appel statique déclenché par self::, parent::, static::, ou, tout en haut de la hiérarchie des classes, forward_static_call(). La fonction get_called_class() peut être utilisée pour récupérer une chaine contenant le nom de la classe appelée, et static:: introduit son espace.

Cette fonctionnalité a été baptisée "late static bindings", avec un point de vue interne. "Late binding", littéralement résolution tardive, vient du fait que les éléments static:: ne seront pas résolus en utilisant la classe où la méthode a été définie, mais celle qui est active durant l'exécution. L'adjectif statique a été ajouté car ce problème s'applique (sans y être limité) aux méthodes statiques.

Limitations de self::

Les références statiques à la classe courante, avec self:: ou __CLASS__, sont résolues en utilisant la classe à laquelle appartiennent les fonctions, celle où elles ont été définies :

Exemple #1 Utilisation de self::

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

class
B extends A {
public static function
qui() {
echo
__CLASS__;
}
}

B::test();
?>

L'exemple ci-dessus va afficher :

A

Utilisation de la résolution statique à la volée

La résolution statique à la volée essaie de dépasser cette limitation en introduisant un mot clé qui fait référence à la classe qui a été appelée durant l'exécution. Pour faire simple, ce mot-clé permet le référencement à B depuis test(), dans l'exemple précédent. Il a été décidé de ne pas introduire de nouveau mot clé, mais plutôt d'utiliser le mot static qui était déjà réservé.

Exemple #2 Utilisation simple de static::

<?php
class A {
public static function
qui() {
echo
__CLASS__;
}
public static function
test() {
static::
qui(); // Ici, résolution à la volée
}
}

class
B extends A {
public static function
qui() {
echo
__CLASS__;
}
}

B::test();
?>

L'exemple ci-dessus va afficher :

B

Note:

Dans les contextes non statiques, la classe appelée sera celle de l'objet. Comme $this-> essayera d'appeler des méthodes privées depuis le même contexte, utiliser static:: pourrait donner des résultats différents. Notez aussi que static:: ne peut faire référence qu'à des attributs/méthodes statiques.

Exemple #3 Utilisation de static:: dans un contexte non statique

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

class
B extends A {
/* foo() sera copiée dans B, par conséquent son contexte sera toujours A
* et l'appel se fera sans problème */
}

class
C extends A {
private function
foo() {
/* La méthode originale est remplacée; le contexte est celui de C */
}
}

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

L'exemple ci-dessus va afficher :

success!
success!
success!


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

Note:

La résolution des statiques à la volée va s'arrêter à un appel statique complètement résolu. D'un autre coté, les appels statiques en utilisant un mot-clé comme parent:: ou self:: vont transmettre l'information appelante.

Exemple #4 Appel avec ou sans transmission

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

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

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

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

C::test();
?>

L'exemple ci-dessus va afficher :

A
C
C

add a note

User Contributed Notes 29 notes

up
166
sergei at 2440media dot com
16 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'
up
61
mhh1422 at hotmail dot com
10 years 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
25
MelkiySoft
6 years ago
<?php

class A
{

}

class
B extends A
{
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
C extends B
{

}

c::foo();
===========================
output:
//new self: object(B)#1 (0) { }
//new parent: object(A)#1 (0) { }
//new static: object(C)#1 (0) { }
up
2
MikeT
2 years ago
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
up
7
backnot
3 years ago
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 A {
private function
foo() {
echo
"success!\n";
}
public function
test() {
$this->foo();
static::
foo();
}
}

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

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

$b = new B();
$b->test();
$c = new C();
$c->test(); // 'success' 'hello world'
?>
up
12
sskaje at gmail dot com
9 years ago
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
b extends a{}
class
c 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"

*/
up
1
aabweber at gmail dot com
2 years ago
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
up
1
Anonymous
2 years ago
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"
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6
tyler AT canfone [dot] COM
16 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.
up
7
steven dot karas+nospam at gmail dot com
14 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);
}

?>
up
11
tamilps2 at gmail dot com
10 years 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
?>
up
9
jakub dot lopuszanski at nasza-klasa dot pl
14 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)
?>
up
7
kx
16 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"

?>
up
7
Andrea Giammarchi
16 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
?>
up
4
adam dot prall at thinkingman dot com
14 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.
up
2
joost dot t dot hart at planet dot nl
15 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

?>
up
3
Taai
12 years 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() );
?>
up
0
5imun at github dot com
2 years ago
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
up
0
sebastien at info-conseil dot fr
16 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::
up
0
deadimp at gmail dot com
16 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;
}
?>
up
0
max at mastershrimp dot com
16 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
up
-1
gern_ at hotmail dot com
16 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;
}
?>
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-2
php at mikebird dot co dot uk
16 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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-3
kenneth at kennethjorgensen dot com
15 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
-2
martinpauly [at] google mail [dot] com
16 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
?>
up
-3
jrfish dot x at gmail dot com
14 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
up
-3
iamscrumpyjack
16 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.
up
-4
Anonymous
16 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
up
-2
5imun at github dot com
2 years ago
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.
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