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 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:
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 referencing 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:
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 A {
private function foo() {
echo "success!\n";
}
public function test() {
$this->foo();
static::foo();
}
}
class
B extends A {
/* foo() will be copied to B, hence its scope will still be A and
* the call be successful */
}class
C extends A {
private function foo() {
/* original method is replaced; the scope of the new one is C */
}
}$b = new B();
$b->test();
$c = new C();
$c->test(); //fails
?>
The above example will output:
success!
success!
success!
Fatal error: Call to private method C::foo() from context 'A' in /tmp/test.php on line 9
Note:
Late static bindings' resolution will stop at a fully resolved static call with no fallback. On the other hand, static calls using keywords like parent:: or self:: will forward the calling information.
Example #4 Forwarding and non-forwarding calls
<?php
class A {
public static function foo() {
static::who();
}
public static function
who() {
echo __CLASS__."\n";
}
}class
B extends A {
public static function test() {
A::foo();
parent::foo();
self::foo();
} public static function
who() {
echo __CLASS__."\n";
}
}
class C extends B {
public static function who() {
echo __CLASS__."\n";
}
}C::test();
?>
The above example will output:
sergei at 2440media dot com ¶
14 years ago
Finally we can implement some ActiveRecord methods:
<?php
class Model
{
public static function find()
{
echo static::$name;
}
}
class
Product extends Model
{
protected static $name = 'Product';
}
Product::find();
?>
Output: 'Product'
mhh2422 at hotmail dot com ¶
8 years ago
For abstract classes with static factory method, you can use the static keyword instead of self like the following:
<?phpabstract class A{
static function
create(){//return new self(); //Fatal error: Cannot instantiate abstract class Areturn new static(); //this is the correct way} }
class
B extends A{
}$obj=B::create();
var_dump($obj);?>
MelkiySoft ¶
4 years ago
<?phpclass 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) { }
sskaje at gmail dot
com ¶
7 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"
*/
backnot ¶
1
year 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'
?>
tamilps2 at gmail dot com ¶
8 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
$fruit->getString(); // Banana
?>
tyler AT canfone [dot] COM ¶
14 years ago
@ php at mikebird
You can pass arguments to your constructor through your getInstance method, assuming you are running php5.
public static function getInstance($params = null) {
if (self::$objInstance == null) {
$strClass = static::getClass();
self::$objInstance = new $strClass($params);
}
return self::$objInstance;
}
This would pass the params to your constructor. Love for php.
adam dot prall at
thinkingman dot com ¶
12 years ago
Just a quick reminder to always check your syntax. While I love LSB, I thought it wasn't working:
static::$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.
kx ¶
14
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.
<?phpclass a {
static public function test() {
print get_called_class();
}
}
class
b extends a {
}a::test(); // "a"
b::test(); // "b"?>
steven dot karas+nospam at gmail dot com ¶
12 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.
<?phpfunction & 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);
}?>
Andrea Giammarchi ¶
14 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
?>
jakub dot lopuszanski at
nasza-klasa dot pl ¶
11 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)
?>
joost dot t dot hart at planet dot
nl ¶
13 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...
<?phpclass 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?>
deadimp at gmail dot com ¶
14 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;
}
?>
Taai ¶
10 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() );
?>
5imun at github dot com ¶
2 months 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
5imun at github
dot com ¶
2 months 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
FooFoo
Bar
Bar
Notice how $bar->getA1() returns "Foo" instead of "Bar" that many people would expect to see.
aabweber at gmail dot
com ¶
6 months 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
Anonymous ¶
7
months 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"
gern_ at hotmail dot com ¶
14 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;
}
?>
sebastien at info-conseil dot fr ¶
14 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::
php at
mikebird dot co dot uk ¶
14 years ago
This should make life easier and neater if you have a project with a lot of singleton classes e.g.
<?phpclass 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.
iamscrumpyjack
¶
14 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.
martinpauly [at] google mail [dot] com ¶
14 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
?>
Anonymous ¶
11 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();
?>
tfn dot yldrm at hotmail dot
com ¶
11 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
?>
jrfish dot x at gmail dot
com ¶
11 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
kenneth at kennethjorgensen dot
com ¶
13 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.
<?phpabstract 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 === $b2)
echo "All good\n";
else
echo "FAIL!\n";?>
You probably noticed the use of self:: rather than static::, this is because we want the static variable to be private, and using static:: will not allow us to do that.
tom ¶
13 years
ago
Something you may find useful for passive code-testing:
<?php
class BaseClass {
function __get($id) {
throw new Exception("Trying to access undefined property '$id'.");
}
function __set($id) {
throw new Exception("Trying to access undefined property '$id'.");
}
}
class
MyClass extends BaseClass {
// my implementation
}
?>
Using these magic function as described above will help you to find classes that try to access an undefined (and undocumented) class-member. In most cases: this is an error based on misspelled member names.
Anonymous ¶
14 years ago
Trying to recreate an inheritable static part for an object through a singleton pattern.
<?php
/**
* "Inheritable static" for PHP < 5.3
* << Library/Inheritable.php >>
*/abstract class Inheritable_Static extends Singleton
{
}
abstract class
Inheritable
{
public static function getStatic($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
Late static binding was a feature introduced with php 5.3. It allows us to inherit static methods from a parent class, and to reference the child class being called.
The compiler performs a process called binding when an object is assigned to an object variable. The early binding (static binding) refers to compile time binding and late binding (dynamic binding) refers to runtime binding.
This is called late static binding. This feature of late static binding was introduced in PHP 5.3 and above, previous versions will show a fatal error.
