Essential for beginners to learn the framework in 2017: Detailed explanation of namespaces in the Thinkphp5 framework tutorial

ThinkPHP is a fast, compatible and simple lightweight domestic PHP development framework. Using ThinkPHP framework can greatly simplify our development process and save time. . This article is for PHP Chinese to teach everyone a very important concept in ThinkPHP: Namespace.

Namespace

ThinkPHP uses namespace definition and automatic loading of class library files, effectively solving the problem of multi-module and Composer Namespace conflicts between class libraries are solved, and a more efficient automatic loading mechanism for class libraries is implemented.

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## Because functions are not supported in

PHP syntax Overloading mechanism, what should I do if there are two methods with the same name in an application? In the Yii framework, in order to avoid problems caused by duplicate names, all classes have the word C in front of them, and the concept of namespaces was introduced in ThinkPHP. There are a few points that require special attention:

a) The namespace is a virtual definition space, not a real directory

b) The delimiters of the namespace are all backslashes\

c) Namespace is only valid for functions, classes, and constants (const-defined constants, non-define-defined constants).

d) The namespace has three access methods: unqualified name access method; qualified name access method; fully qualified name access method.

The following will be explained in detail one by one.

1. Namespace is only valid for functions, classes, and constants (const-defined constants, non-define-defined constants).

# Here we declare two namespaces space1 and space2 , there are function getmsg() with the same name, constant a with the same name, and class Animal with the same name under the two namespaces. Because they are in different namespaces, no errors will occur. We open it in the browser and get the following output: helloworld.

What if we try to use define to define two constants with the same name?

When opened in the browser, the following error is reported:

So the namespace is only valid for functions, classes, and constants (const-defined constants, non-define-defined constants).

2. Multi-level namespaces and three access methods

The namespaces space1 and space2 declared above are both single-level Namespace, a namespace in the shape of space1\space2\space3 is a multi-level namespace, and the separator is \. The following introduces three namespace access methods:

1. Unqualified name access method

When accessed in unqualified name access mode, the functions under the current namespace are accessed (the same applies to classes and constants), so the output result of the above code is: world.

2. Fully qualified name access method

If you want to access getmsg() under name1\space1 in the name2\space2 namespace method, you can use fully qualified name access (equivalent to absolute path access).

#So the output of the above code is: hello.

3. Qualified name access method

The difference between qualified name access method and fully qualified name access method is only in the first \ . If the above example uses qualified name access, change the last line to: name1\space1\getmsg();

At this time, we open it in the browser and find the following error:

Prompts that we cannot find the getmsg() function under the namespace name2\space2\name1\space1. The reason is that Limited name access method is equivalent to relative path access. We use qualified name access method to access under the current namespace: name1\space1\getmsg(), which will search for name1\space1 under the current namespace. The getmsg() function will report an error if it cannot be found. Therefore, if we declare another namespace named: name2\space2\name1\space1, the above access can be executed normally, as follows:

The output result is: hello -world.

3. Introduction mechanism of namespace and space class elements

1. Introduction of namespace

Through the above example, we can see that if we want to use functions, constants or class elements in another namespace in the current namespace, we need to use fully qualified access to access and write code It is relatively cumbersome, so we can introduce a namespace and then use qualified name access to simplify the access process.

##The output result is: hello dog

2. Introduction of space elements

Similar to the introduction of namespaces, use the use keyword to introduce space elements, and then use unqualified access directly. Just visit. However, a class with the same name as the imported class cannot exist in the current namespace, otherwise an error will occur.

The output result is: dog rhubarb.

4. Public space

If we do not use the namespace keyword to declare a namespace, it belongs to the public space .

Here we create two php files, 1.php and 2.php, 1.php namespace is name1\space1, 2.php is the public space .

1.php：

namespace  name1\space1;
header("content-type:text/html;charset=utf-8");
class Animal
{
    public $obj = 'dog';
    static $name = '大黄';
}
function getmsg()
{
    echo 'hello';
}

const MN = 123;

//在命名空间中引入公共命名空间

include ('./2.php');

getmsg();       //访问的是当前空间下的getmsg()函数
echo &#39;</br>&#39;;
\getmsg();      //访问的是公共命名空间（即2.php文件）下的getmsg()函数

echo &#39;</br>&#39;;
echo MN;          //会先在当前命名空间下寻找MN常量，如果找到就输出，如果找不到，就会去公共命名空间寻找MN常量
echo &#39;</br>&#39;;
echo  \MN;         //访问的是公共命名空间（即2.php文件）下的MN常量

2.php：

//没有指定命名空间，则其属于公共命名空间
function getmsg()
{
    echo 'world';
}

const MN = '456';

Open 1.php in your browser , the output result is:

hello

world
123
456

5. Namespace is a virtual definition space, not a real directory

In thinkphp5.0, the namespace is a virtual definition space, not a real directory. It's just that when the official declares the namespace, the name of the namespace deliberately corresponds to the directory structure.

#For example, we open the Index.php file in the application/index/controller folder, and its namespace is: app\index\controller. does not exist in the directory structure.

Namespace alias

The framework allows you to define aliases for namespaces, for example:

namespace app\index\model;
use think\Model;
class User extends Model
{
}

The original calling method in the controller is:

namespace app\index\controller;
use app\index\model\User;
class Index
{
 public function index()
 {
  $user = new User();
 }
}

If we register the namespace alias in the application public file as follows:

\think\Loader::addNamespaceAlias('model','app\index\model');

Then, the above controller code is Can be changed to:

namespace app\index\controller;
use model\User;
class Index
{
 public function index()
 {
  $user = new User();
 }
}

相关资料推荐： 

1. 什么是php命名空间？命名空间用法实例详解

2. php命名空间与自动加载类用法实例详解

3. php关于use、命名空间、引入类文件和自动加载类的实例详解