Range resolution operator (::)

The scope resolution operator (also known as Paamayim Nekudotayim) or more simply a pair of colons can be used to access static members, class constants, and can also be used to override properties and methods in a class.

When referencing these items outside of the class definition, use the class name.

Since PHP 5.3.0, classes can be referenced through variables whose values ​​cannot be keywords (such as self, parent and static).

The choice of Paamayim Nekudotayim as the name of the double colon operator seems a bit strange. However, this was a decision the Zend development team made when writing Zend Engine 0.5 (used in PHP 3). In fact, this word in Hebrew means double colon.

Example #1 Using :: operator

<?php
class MyClass {
    const CONST_VALUE = &#39;A constant value&#39;;
}

$classname = &#39;MyClass&#39;;
echo $classname::CONST_VALUE; // 自 PHP 5.3.0 起

echo MyClass::CONST_VALUE;
?>

self, parent and static These three special keywords are Used to access properties or methods within a class definition.
Example #2 Use inside the class definition ::

<?php
class OtherClass extends MyClass
{
    public static $my_static = &#39;static var&#39;;

    public static function doubleColon() {
        echo parent::CONST_VALUE . "\n";
        echo self::$my_static . "\n";
    }
}

$classname = &#39;OtherClass&#39;;
echo $classname::doubleColon(); // 自 PHP 5.3.0 起

OtherClass::doubleColon();
?>

Example #3 Call the method of the parent class

<?php
class MyClass
{
    protected function myFunc() {
        echo "MyClass::myFunc()\n";
    }
}

class OtherClass extends MyClass
{
    // 覆盖了父类的定义
    public function myFunc()
    {
        // 但还是可以调用父类中被覆盖的方法
        parent::myFunc();
        echo "OtherClass::myFunc()\n";
    }
}

$class = new OtherClass();
$class->myFunc();
?>

The above introduces the range parsing operator (::), including the relevant content. I hope it will be helpful to friends who are interested in PHP tutorials.