Detailed explanation of php late static binding examples
The working principle of late static binding is to store the class name in the previous "non-forwarding call" (non-forwarding call
).
When making a static method call, the class name is the one explicitly specified (usually on the left side of the :: operator);
When a non-static method call is made, it is the class to which the object belongs.
The so-called "forwarding call" (
forwarding call
) refers to static calls made in the following ways:self::
,parent::
,static::
andforward_static_call()
. You can use theget_called_class()
function to get the class name of the called method, andstatic::
points out its scope.
limitations of self::
Use
self::
or__CLASS__
for a static reference to the current class, depending Define the class in which the current method is located:
Example:
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 ();
Result:
A
static (late static binding)
Late static binding was intended to circumvent the limitation by introducing a new keyword representing the class that was initially called by the runtime. Simply put, this keyword allows you to refer to class B instead of A when calling test() in the above example. It was finally decided not to introduce new keywords, but to use the already reserved
static
keywords.
Example:
<?phpclass A { public static function who() { echo __CLASS__; } public static function test() { static::who(); // 后期静态绑定从这里开始 } }class B extends A { public static function who() { echo __CLASS__; } } B::test();?>
Result:
B
The difference between static and $this
In a non-static environment, what is called The class of is the class to which the object instance belongs. Since
$this->
will try to call the private method in the same scope,static::
may give different results. Another difference is that static properties can only be called withstatic::
.
Example: Calling a private method
<?phpclass 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
Result:
success! success! success! Fatal error: Call to private method C::foo() from context 'A' in /tmp/test.php on line 9
Forwarded and non-forwarded calls
Analysis of late static binding Will continue until a fully parsed static call information is obtained. On the other hand, if the static call is made using
parent::
orself::
the call information will be forwarded.
Example:
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();
Result:
ACC
Related recommendations:
PHP late static binding example sharing
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