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This article mainly explains "how to use and define namespaces in PHP", interested friends may wish to take a look. The method introduced in this paper is simple, fast and practical. Let's learn how to use and define namespaces in PHP!

Namespaces are an abstract concept. For example, in our daily life, directories are used to group related files in operating systems. For files in directories, they play the role of namespaces.

So what is a namespace? In fact, namespaces can be understood as a way to encapsulate things. Classes, functions, and constants in PHP cannot have the same name. In order to prevent them from having the same name and solve the problem of the same name, namespaces are needed.

In PHP, namespaces are mainly used to resolve naming conflicts between user-written code and PHP internal or third-party classes, functions, and constants. There are always too many files that may be named repeatedly. There are also very short names for long identifier names, which will improve the readability of the code.

So how are namespaces declared, defined and used? Let's look at how namespaces should be defined!

define the namespace

Any correct code in PHP can be included in namespaces, but only classes, functions, constants, etc. are affected by namespaces.

We complete the namespace definition with the namespace keyword, which has the following syntax:

namespace namespace name;

Examples are as follows:

Define two namespaces:

Define child namespaces

Namespaces in PHP are similar to directories and files, allowing hierarchical namespace names to be specified. Therefore, namespace names can be defined in a hierarchical manner, with the syntax as follows:

namespace App\Model;namespace App\Controller\Home;

Examples are as follows:

In the example above, the constant MyProject\Sub\Level\CONNECT_OK, the class MyProject\Sub\Level\Connection, and the function MyProject\Sub\Level\Connect were created

Define multiple namespaces in the same file

There are two syntax formats that allow you to define multiple namespaces in a single file, examples of which are as follows:

The first is a simple syntax combination

Then there are braces {}

From the above introduction, we already know how to define namespaces, just defining namespaces is not enough, we use it in PHP is more important, then look at how to use namespaces.

use the namespace

Before we understand how namespaces should be used, we should understand how to know which namespace element to use in PHP, and then we need to understand how namespace element access works in PHP. First of all we don't know much about PHP, but file systems we can summarize three ways to access files:

Relative file names, relative path names, and absolute path names.

The elements of PHP namespaces use the same principle, for example, class names under namespaces can be derived in three ways:

Unqualified names, or class names without prefixes, such as $a = new test() or test, resolve to currentnamespace\test if the current namespace is currentnamespace. If the code for test is global and does not contain code from any namespace, then test resolves to test.

Qualified names, or names containing prefixes, such as $a = new namespace\test(), resolve to currentnamespace\subnamespace\test if the current namespace is currentnamespace, and resolve to subnamespace\foo if the code of test is global and does not contain code from any namespace.

Fully qualified names, or names that include global prefix operators, such as $a = new \currentnamespace\test(), in which case test always resolves to the literal name currentnamespace\test in the code.

Here is an example of using these three methods. We need two PHP source files, demo.php and index.php. The sample code is as follows:

In the above example, it is important to note that any global class, function, or constant can be accessed with a fully qualified name, such as\strlen() or\Exception.

alias, import

PHP allows external namespaces to be used by alias references or imports, an important feature of namespaces.

In PHP, namespaces can be imported and aliases can be set by combining the use keyword with as. Its syntax is as follows:

use namespace as alias;

Examples are as follows:

One thing to note is that the import operation affects only unqualified and qualified names. Fully qualified names are not affected by imports because they are deterministic.

At this point, I believe everyone has a deeper understanding of "how to use and define namespaces in PHP," so let's actually operate it! Here is the website, more related content can enter the relevant channels for inquiry, pay attention to us, continue to learn!

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