PHP namespace: detailed explanation of aliases and import instances

Aliases and imports can be seen as a shortcut for calling namespaces. Allowing external fully qualified names to be referenced or imported through aliases is an important feature of namespaces. This is somewhat similar to how you can create soft links to other files or directories in a Linux file system. The previous chapter explained the terminology that you need to know about the three names of the space in the namespace: Unqualified name, qualified name, fully qualified name. Only by first understanding these three names and terms can we better learn and understand the aliases of the namespace and the imported content.                        

php namespace supports two ways of using aliases or imports: Use aliases for class names, or use aliases for namespace names. Note that php imports functions or constants. In php, aliases are implemented through the operator use .

The following is an example code using all possible import methods:

<?php
namespace cn\my;  //声明命名空间 cn\my
class User{ }     // 当前空间下声明一个类
namespace shop;   // 在创建一个空间
use cn\my;        //导入一个命名空间
$my_User = new my\User();    //导入命名空间后可使用限定名称调用元素
use cn\my as u;            //命名空间使用别名
$my_User = new u\User();   //使用别名代替空间名
use cn\my\User;              //导入一个类
$my_User = new User();       //导入类后可使用非限定名称调用元素
use cn\my\User as myUser;   // 为类使用别名
$my_User = new myUser();   //使用别名代替空间名
?>

It should be noted that when using use to import, the current space has the same name element, a fatal error will occur.

The code is as follows:

<?php
namespace cn\my;
class User{ }
namespace shop;
class User{ }
class myUser{ }
//导入一个类
use cn\my\User;
// 与当前空间的 User 发生冲突，产生致命错误
$my_user = new User();
// 为类使用别名
use cn\my\User as myUser;
// 与当前空间 myUser 发生冲突，产生致命错误
$my_user = new myUser();
?>

In addition to using aliases and imports, you can also pass the namespace keywords and __NAMESPACE__ Magic constantsAccess elements dynamically. The namespace keyword represents the current space, and the value of the magic constant __NAMESPACE__ is the name of the current space. __NAMESPACE__ can be called dynamically by combining strings.

The sample code is as follows:

<?php
namespace cn\my;  //声明命名空间 cn\my
const PATH = &#39;cn\my&#39;;
class User{ }     // 当前空间下声明一个类
echo namespace\PATH;   //namespace 关键字表示当前空间 cn\my
$User = new namespace\User(); //使用namespace代替 \cn\my
echo __NAMESPACE__;    //魔法常量的值是当前空间名称 cn\my
$User_class =  __NAMESPACE__ . &#39;\User&#39;;  //组合称字符串并调用
$User = new $User_class;
?>

In the above example of dynamic calling, the dynamic calling method is in string form , it should be noted that special characters may be escaped when using double quotes, for example, in "__NAMESPACE__ . "\User" ", "\User" will be escaped in a double-quoted string. In addition, PHP determines the space where the element is located and the import status when compiling the script. When parsing the script, calls in the form of strings can only be considered unqualified names and fully qualified names, and can never be qualified names.

The above is the introduction of php namespace: aliases and imports. Friends need to practice and use the code more. Proficiency in php namespace will be of great help for developing using PHP framework.

【Related tutorial recommendations】

1. "php.cn Dugu Jiujian (4)-php video tutorial"

2. Video tutorial : PHP5.6 extension to namespace: use can import functions and constant spaces

3. A complete set of tutorials on PHP programming from entry to mastery

The above is the detailed content of PHP namespace: detailed explanation of aliases and import instances. For more information, please follow other related articles on the PHP Chinese website!