Type Hinting
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
?>
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.
This feature was named "late static bindings" with an internal perspective in mind. "Late binding" comes from the fact that static:: will no longer 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 A {
public static function who() {
echo __CLASS__;
}
public static function test() {
self::who();
}
}
class B extends A {
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 A {
public static function who() {
echo __CLASS__;
}
public static function test() {
static::who(); // Here comes Late Static Bindings
}
}
class B extends A {
public static function who() {
echo __CLASS__;
}
}
B::test();
?>
The above example will output:
B
Note: static:: does not work like $this for static methods! $this-> follows the rules of inheritance while static:: doesn't. This difference is detailed later on this manual page.
Example #3 static:: usage in a non-static context
<?php
class TestChild extends TestParent {
public function __construct() {
static::who();
}
public function test() {
$o = new TestParent();
}
public static function who() {
echo __CLASS__."\n";
}
}
class TestParent {
public function __construct() {
static::who();
}
public static function who() {
echo __CLASS__."\n";
}
}
$o = new TestChild;
$o->test();
?>
The above example will output:
TestChild TestParent
Note: Late static bindings' resolution will stop at a fully resolved static call with no fallback. On the other hand, static calls using keywords like parent:: or self:: will forward the calling information.
Example #4 Forwarding and non-forwarding calls
<?php
class A {
public static function foo() {
static::who();
}
public static function who() {
echo __CLASS__."\n";
}
}
class B extends A {
public static function test() {
A::foo();
parent::foo();
self::foo();
}
public static function who() {
echo __CLASS__."\n";
}
}
class C extends B {
public static function who() {
echo __CLASS__."\n";
}
}
C::test();
?>The above example will output:
A C C
Edge cases
There are lots of different ways to trigger a method call in PHP, like callbacks or magic methods. As late static bindings base their resolution on runtime information, it might give unexpected results in so-called edge cases.
Example #5 Late static bindings inside magic methods
<?php
class A {
protected static function who() {
echo __CLASS__."\n";
}
public function __get($var) {
return static::who();
}
}
class B extends A {
protected static function who() {
echo __CLASS__."\n";
}
}
$b = new B;
$b->foo;
?>
The above example will output:
B
add a note
User Contributed NotesLate Static Bindings
joost dot t dot hart at planet dot nl
21-Aug-2009 01:34
21-Aug-2009 01:34
tom
03-Jul-2009 01:28
03-Jul-2009 01:28
Something you may find useful for passive code-testing:
<?php
class BaseClass {
function __get($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.
kenneth at kennethjorgensen dot com
30-Mar-2009 10:19
30-Mar-2009 10:19
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.
lazybones_senior
01-Oct-2008 07:30
01-Oct-2008 07:30
WHOA... KEEP IT SIMPLE!
Remember, when you write a class definition, you are creating a new "type" of object. And when you extend those classes, you are creating a heirarchy. To get to the point... all the class defs below work together to provide a solid organization of data.
<?php
abstract class Animal {
protected $type, $name;
public function __construct($aType, $aName) {
$this->type = $aType;
$this->name = $aName;
}
public function __toString() {
return "Animal [type=$this->type, name=$this->name]";
}
}
class Dog extends Animal {
public function __construct($aName) {
parent::__construct("Dog", $aName);
}
}
class Cat extends Animal {
public function __construct($aName) {
parent::__construct("Cat", $aName);
}
}
echo 'My dog: ' . (new Dog('Sam')) . '<br>';
echo 'My cat: ' . (new Cat('Fluffy')) . '<br>';
echo 'Your dog: ' . (new Dog('Walter')) . '<br>';
echo 'Yout cat: ' . (new Cat('Ginger'));
?>
My dog: Animal[type=Dog, name=Sam]
My cat: Animal[type=Cat, name=Fluffy]
Your dog: Animal[type=Dog, name=Walter]
Yout cat: Animal[type=Cat, name=Ginger]
... and notice the property called $type, is the same as using __CLASS__ in most of the previous posts, but without the complexities of the PHP language.
gern_ at hotmail dot com
18-Sep-2008 02:51
18-Sep-2008 02:51
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;
}
?>
kx
14-Sep-2008 04:39
14-Sep-2008 04:39
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"
?>
iamscrumpyjack
07-Sep-2008 04:01
07-Sep-2008 04:01
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.
sebastien at info-conseil dot fr
17-Jul-2008 02:26
17-Jul-2008 02:26
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::
Anonymous
12-Jul-2008 07:49
12-Jul-2008 07:49
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
Andrea Giammarchi
21-Jun-2008 08:06
21-Jun-2008 08:06
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
?>
martinpauly [at] google mail [dot] com
18-Jun-2008 12:54
18-Jun-2008 12:54
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
?>
deadimp at gmail dot com
05-Jun-2008 05:39
05-Jun-2008 05:39
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 $temp;
}
?>
tyler AT canfone [dot] COM
05-Jun-2008 05:48
05-Jun-2008 05:48
@ php at mikebird
You can pass arguments to your constructor through your getInstance method, assuming you are running php5.
public static function getInstance($params = null) {
if (self::$objInstance == null) {
$strClass = static::getClass();
self::$objInstance = new $strClass($params);
}
return self::$objInstance;
}
This would pass the params to your constructor. Love for php.
sergei at 2440media dot com
28-May-2008 08:22
28-May-2008 08:22
Finally we can implement some ActiveRecord methods:
<?php
class Model
{
public static function find()
{
echo static::$name;
}
}
class Product extends Model
{
protected static $name = 'Product';
}
Product::find();
?>
Output: 'Product'
php at mikebird dot co dot uk
23-Apr-2008 03:39
23-Apr-2008 03:39
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.
max at mastershrimp dot com
10-Apr-2008 10:24
10-Apr-2008 10:24
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