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This article focuses on "how namespaces exist in PHP". Friends who are interested might as well take a look. The method introduced in this paper is simple, fast and practical. Let's let the editor take you to learn how namespaces exist in PHP.

How does Namespace exist in PHP (1)

Namespaces actually existed in PHP5.3 as early as possible. However, most students may only come into contact with the content of namespaces in the use of various frameworks, and of course, modern development is inseparable from these frameworks that can be produced quickly. This time we will not analyze the concept and use of namespaces from a framework perspective, but from a simple code perspective.

First, we need to define what a namespace is.

In fact, just like operating system directories, namespaces are designed to solve the problem that the same folder in the operating system cannot have the same file name. Suppose we have only one file and one directory, then there can be no two identical files in this directory. If there is a file with exactly the same name, the operating system doesn't know which file we should open. Similarly, we can't have a function or class name with the same name in a PHP file, and PHP doesn't know which function or class we're calling.

After understanding the above, let's take a look at the syntax of the namespace, which is actually very similar to the definition of our directory.

Namespace A\ B\ C

The definition of this namespace indicates that the current namespace is A\ B\ C. It's like a folder like C:\ A\ B\ C. Just talk but don't practice fake tricks, just go to the code and have a look:

/ / file1.php

Namespace FILE1

Const CONST_A = 2

Function testA () {

Echo 'FILE1\ testA ()', PHP_EOL

}

Class objectA {

Function test () {

Echo 'FILE1\ ObjectA', PHP_EOL

}

}

/ / file2.php

Namespace FILE2

Const CONST_A = 3

Function testA () {

Echo 'FILE2\ testA ()', PHP_EOL

}

Class objectA {

Function test () {

Echo 'FILE2\ ObjectA', PHP_EOL

}

}

We created these two php files in the namespace directory. The function and class names are the same, but different namespaces are defined, one is FILE1 and the other is FILE2.

Namespace A

Include 'namespace/file1.php'

Include 'namespace/file2.php'

Use FILE1, FILE2

Use FILE1\ objectA as objectB

Const CONST_A = 1

Function testA () {

Echo'A\ testA ()', PHP_EOL

}

Class objectA {

Function test () {

Echo'a\ ObjectA', PHP_EOL

}

}

/ / current namespace

Echo CONST_A, PHP_EOL; / / 1

TestA (); / / A\ testA ()

$oA = new objectA ()

$oA- > test (); / / A\ ObjectA

/ / FILE1

Echo FILE1\ CONST_A, PHP_EOL; / / 2

FILE1\ testA (); / / FILE1\ testA ()

$oA = new FILE1\ objectA ()

$oA- > test (); / / FILE1\ ObjectA

$oB = new objectB ()

$oB- > test (); / / FILE1\ ObjectA

/ / FILE2

Echo FILE2\ CONST_A, PHP_EOL; / / 3

FILE2\ testA (); / / FILE2\ testA ()

$oA = new FILE2\ objectA ()

$oA- > test (); / / FILE2\ ObjectA

In the test code, we define the current namespace as A. And include file1.php and file2.php. The same functions and class names are also defined in this file as in file1.php and file2.php. Next we call these static variables, functions, and classes in turn.

By default, static variables, functions, and classes call the content under the current namespace after using FILE1\ and FILE2\. What is called is that the content under the specified namespace needs to be introduced into the namespace using use, otherwise you cannot use the content in the namespace use to specify aliases for the namespace or the classes in it using the as keyword

The use of namespaces is actually that simple. You can see that we can use the same function or class name in different namespaces. This is the basis of all kinds of modern development frameworks. It is also one of the main reasons why composer can be implemented.

Next, let's try a question that meets our expectations, that is, whether two files with the same namespace can define the same class name.

/ / file1-1.php

Namespace FILE1

Const CONST_A = 1.1

Function testA () {

Echo 'FILE1-1\ testA ()', PHP_EOL

}

Class objectA {

Function test () {

Echo 'FILE1-1\ ObjectA', PHP_EOL

}

}

We define a file1-1.php and use the same FILE1 namespace as file1.php. Then include it into the test code with file1.php.

Include 'namespace/file1.php'

Include 'namespace/file1-1.phpads; / / Cannot redeclare FILE1\ testA ()

Well, the error is reported directly at run time, and the function name with the same name cannot be repeatedly defined. If the function is commented out, it will continue to report that the class name cannot be repeated. Let's define another file1-2.php, this time using the FILE1 namespace, but the content is different.

/ / file1-2.php

Namespace FILE1

Const CONST_A = 1.2

Function testA1_2 () {

Echo 'FILE1-2\ testA ()', PHP_EOL

}

Class objectA1_2 {

Function test () {

Echo 'FILE1-2\ ObjectA', PHP_EOL

}

}

Of course there will be no problem. The two files are in the same namespace, but have different capabilities, which is a full OK operation.

Include 'namespace/file1.php'

Include 'namespace/file1-2.php'

Use FILE1

/ / FILE1

Echo FILE1\ CONST_A, PHP_EOL; / / 2

FILE1\ testA (); / / FILE1\ testA ()

$oA = new FILE1\ objectA ()

$oA- > test (); / / FILE1\ ObjectA

/ / FILE1_2

Echo FILE1\ CONST_A, PHP_EOL; / / 3

FILE1\ testA1_2 (); / / FILE1-2\ testA ()

$oA = new FILE1\ objectA1_2 ()

$oA- > test (); / / FILE1-2\ ObjectA

Test code: https://github.com/zhangyue0503/dev-blog/blob/master/php/202001/source/PHP%E4%B8%AD%E5%91%BD%E5%90%8D%E7%A9%BA%E9%97%B4%E6%98%AF%E6%80%8E%E6%A0%B7%E7%9A%84%E5%AD%98%E5%9C%A8%EF%BC%9F%EF%BC%88%E4%B8%80%EF%BC%89.php

Reference document: https://www.php.net/manual/zh/language.namespaces.rationale.phphttps://www.php.net/manual/zh/language.namespaces.definition.php

At this point, I believe you have a deeper understanding of "how namespaces exist in PHP". You might as well do it in practice. Here is the website, more related content can enter the relevant channels to inquire, follow us, continue to learn!

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