Detailed example of using range resolution operator in PHP

Object-oriented Some of its own operators are used in programming, such as ->. This symbol is used to access its own members in the object. The other one is the range resolution operator: two colons connected together (::). This notation is used to access members within a class (not within an object). The usage is as follows:

ClassName::methodName();
ClassName::propertyName;

This structure may be used in two places:

1. When using a class, the parent class and the subclass have the same Attributes and methods, use this to avoid confusion.

2. When outside the class, use this operator to access the members of the class without creating an object.

Just as we can use $this in a class to refer to an instance of the current object, the keyword self is used as a reference to the current class.

class SomeClass {
    function construct() {
        self::do();
    }

    protected function do(){
        echo "done!";
    }
}

In this code, self::do() will trigger the do() method of the current class.

To reference a member of the parent class, you can use the keyword parent and the range resolution operator to reference:

class SomeOtherClass extends SomeClass {
    function construct() {
        parent::do();
    }
}

In most cases, we use the range resolution operator to Access the overridden method. We can also use it to access static and constant members.

Note: Like static properties, class constants can be accessed by all instances of the class (or its subclasses). But its value cannot be changed. Class constants are created using the const keyword , followed by the constant name (without the dollar sign). Constants cannot be accessed through objects, such as $obj->PI or $obj::PI, but we can use ClassName::CONSTANT_NAME anywhere. You can also use self::CONSTANT_NAME in methods within a class.

Sample program:

<?php  
	class Rectangle {
		protected static $_count = 0;
		protected $width;
		protected $height;

		function construct($width, $height) {
			$this->width = $width;
			$this->height = $height;
			self::$_count++;
			echo "已成功创建".self::$_count."个Rectangle对象<br>";
		}

		function destruct() {
			echo "销毁一个Rectangle对象<br>";
		}

		function getArea() {
			echo "Rectangle面积是:".($this->width * $this->height."<br>");
		}

		function getConunt() {
			return self::$_count;
		}
	}

	class Square extends Rectangle {
		function construct($side) {
			$this->width = $side;
			$this->height = $side;
			parent::$_count++;
			echo "已成功创建".parent::$_count."个Rectangle(Square)对象<br>";
		}
	}

	$rec = new Rectangle(10, 5);
	$rec->getArea();

	$square = new Square(10);
	$square->getArea();

?>

Running results:

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