什么是"::" PHP中的符号用于? [英] what is the "::" notation in php used for?

问题描述

我正在查看一些php代码，并且看到了"::"符号，表示我不知道这意味着什么...还有&是什么.在通话的前面

I am looking through some php code and I see this "::" notation that i have no idea what it means...also what the the & in the front of the call

$mainframe =& JFactory::getApplication('site');
$sql="SELECT rt.member_id ,rt.commission,rt.sales,kt.store_id,kt.user_id FROM jos_report
rt JOIN jos_kingdom_tickets kt WHERE rt.member_id=kt.ticket_id";
$db =& JFactory::getDBO();

预先感谢

推荐答案

::，范围解析运算符，用于引用类的静态成员和常量.它还用于引用超类的构造函数.以下代码说明了范围解析运算符的几种不同用法:

::, the scope resolution operator, is used for referencing static members and constants of a class. It is also used to reference a superclass's constructor. Here is some code illustrating several different uses of the scope resolution operator:

<?php
class A {
    const BAR = 1;
    public static $foo = 2;
    private $silly;

    public function __construct() {
         $this->silly = self::BAR;
    }
}

class B extends A {
    public function __construct() {
        parent::__construct();
    }

    public static function getStuff() {
         return 'this is tiring stuff.';
    }
}

echo A::BAR;
echo A::$foo;
echo B::getStuff();
?>

一些琐事:范围解析运算符也称为"paamayim nekudotayim"，意思是希伯来语中的两个点两次".

A little trivia: The scope resolution operator is also called "paamayim nekudotayim", which means "two dots twice" in hebrew.

&不会做任何有用的事情，应将其删除.在php 4中，这曾经是必须的，以确保未使用返回对象的副本.在php 5中，除非调用 clone ，否则不会创建对象副本.因此，不需要&.仍然有一种情况，&在php 5中仍然有用:在遍历数组的元素并修改值时，必须使用&运算符来影响数组的元素.

& in the context of your example isn't doing anything useful if you are using php 5 or greater and should be removed. In php 4, this used to be necessary in order to make sure a copy of the returned object wasn't being used. In php 5 object copies are not created unless clone is called. And so & is not needed. There is still one case where & is still useful in php 5: When you are iterating over the elements of an array and modifying the values, you must use the & operator to affect the elements of the array.

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