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:
<?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 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.
<?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:
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.
<?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
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.
<?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
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