php的scope是什么意思,PHP之 范围解析操作符Scope Resolution Operator (::)

The Scope Resolution Operator (also

called Paamayim Nekudotayim) or in simpler terms, the double colon,

is a token that allows access to static, constant, and overridden

properties or methods of a class.

When referencing these items from

outside the class definition, use the name of the class.

As of PHP 5.3.0, it's possible to

reference the class using a variable. The variable's value can not

be a keyword (e.g. self, parent and static).

Paamayim Nekudotayim would, at

first, seem like a strange choice for naming a double-colon.

However, while writing the Zend Engine 0.5 (which powers PHP 3),

that's what the Zend team decided to call it. It actually does mean

double-colon - in Hebrew!

Example #1 :: from outside the class

definition

class MyClass {

const CONST_VALUE = 'A constant

value';

}

$classname = 'MyClass';

echo $classname::CONST_VALUE; // As

of PHP 5.3.0

echo MyClass::CONST_VALUE;

?>

Three special keywords self, parent

and static are used to access properties or methods from inside the

class definition.

Example #2 :: from inside the class

definition

class OtherClass extends

MyClass

{

public static $my_static = 'static

var';

public static function doubleColon()

{

echo parent::CONST_VALUE .

"\n";

echo self::$my_static . "\n";

}

}

$classname = 'OtherClass';

echo $classname::doubleColon(); //

As of PHP 5.3.0

OtherClass::doubleColon();

?>

When an extending class overrides

the parents definition of a method, PHP will not call the parent's

method. It's up to the extended class on whether or not the

parent's method is called. This also applies to Constructors and

Destructors, Overloading, and Magic method definitions.

Example #3 Calling a parent's

method

class MyClass

{

protected function myFunc() {

echo "MyClass::myFunc()\n";

}

}

class OtherClass extends

MyClass

{

// Override parent's

definition

public function myFunc()

{

// But still call the parent

function

parent::myFunc();

echo "OtherClass::myFunc()\n";

}

}

$class = new OtherClass();

$class-&gtmyFunc();

?>