What is a namespace in PHP? How to use namespaces?

The previous article introduced you to "PHP Advanced Syntax-What is Trait?" How do we use it? What are his characteristics? 》, this article continues to introduce to you what is a namespace in PHP? How to use namespaces?

Namespace:

If the Person class appears in a file, can another Person class be defined?

The namespace is the folder.

You can have the same class name under different namespaces

namespace: namespace

use: use

First we create a new file. We have defined a person class in the file, so can we still see a person class? We take the code as an example for debugging. The code is as follows:

<?php
   class person
   {
   }
   
   class person
   {
   }
?>

The results are as follows:

We base The results show that the code reports an error that the person class cannot be defined repeatedly. This is an obvious error. We are not allowed to have two identical files in the same file, but if we want to have the same class name, we can reference the namespace. the concept of.

Next we start using namespaces. For the code we just wrote, we wrote the first person under one namespace, and I wrote the second person under another namespace. This Then we can define two person classes at the same time. The namespace is written as follows: In addition, we need to give the namespace a name, so the code we just wrote is in the namespace we just defined. Inside, executing this code will still report an error, so we need to define a namespace for the second person class, and then we define a method (function) in the first class and the second class respectively. At this time we define Two classes have the same name, but are not in the same namespace. The specific code is as follows:

<?php
namespace love;
   class Person
   {
     function pome()
     {
       echo &#39;我明白你会来，所以我等<br />&#39;;
     }
   }
   namespace like;
   class Person
   {
     function pome()
     {
     echo &#39;不须耳鬓常厮伴，一笑低头意已倾<br />&#39;;
   }
   }
?>

The result is as follows:

The result display is correct; no error is reported;

If we want to output the code content we just wrote, we need to create a new person object, otherwise we will not know which one is output person class, the code is as follows:

 $ming = new Person();
   $ming ->pome();

The result is as follows:

Note: When we create the object, we name it there space;

If we want to output the contents of the first namespace, we need to write like this:

$niu = new \love\Person();
  $niu->pome();

The result is as follows:

1. The naming of the first namespace: there cannot be any code in front of it

2. Root space and subspace

Root space

Your hello space is actually

\hello .

Your world space is actually

\world

You are in the world space

hello\Dog ===> world\hello\Dog

3. use use, as use

use \hello\test\Dog as SmallDog;
use
\world\Dog as BigDog;

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