use keyword in PHP

php editor Strawberry will give you an in-depth understanding of the use keyword in PHP. The use keyword plays an important role in PHP. It is mainly used to import namespaces to make the code more concise and readable. Through the use keyword, classes, functions or constants from other namespaces can be introduced into the current scope, making it easier for developers to call them directly in the code and improving the maintainability and readability of the code. In the process of learning and using PHP, mastering the usage of the use keyword is crucial to improving programming efficiency and code quality.

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Introduction and implementation of namespace in php

A namespace in PHP is a tag that contains a block of code. We can use namespaces to access specific blocks of code from elsewhere in the project.

For example, a namespace can contain blocks of code such as classes, functions, constants, etc.

Namespaces mainly solve two problems. all these are:

• Namespaces avoid name conflicts between classes or functions. For example, ambiguity may arise when a user-defined function matches the name of a core PHP function or library function.
• Namespaces allow better communication and organization between modules during the project. We can alias components for better readability.

Let's look at an example of how namespaces work. Create a class Greetings and write a constructor in it.

Display the message Hello everyone! inside the constructor. Save the file as greetings.php.

Next, create another file in the same directory as index.php. First, require greetings.php using the require function.

Then, create a variable $hello and instantiate the Greetings class instance as $hello = new Greetings.

When we serve the index.php file, it gives an error, Class 'Greetings' not found. To solve this problem we can use namespaces.

To do this, create the namespace subodh\project in the greetings.php file. Next, in the index.php file, use the namespace subodh\project before the class Greetings.

This time, the message Hello everyone! is displayed. This is how you use namespaces to organize components in your project.

We can similarly use namespaces to organize functions and variables.

<code>
<code class="php hljs" data-lang="php"><span style="display:flex;"><span><span style="color:#008000;font-weight:bold">namespace</span> subodh\project;
</span></span><span style="display:flex;"><span>
</span></span><span style="display:flex;"><span><span style="color:#008000;font-weight:bold">class</span> <span style="color:#00f;font-weight:bold">Greetings</span>{
</span></span><span style="display:flex;"><span><span style="color:#008000;font-weight:bold">public</span> <span style="color:#008000;font-weight:bold">funct<strong class="keylink">io</strong>n</span> __construct(){
</span></span><span style="display:flex;"><span><span style="color:#008000;font-weight:bold">print</span>(<span style="color:#ba2121">"Hello everyone!"</span>)<span style="color:#666">.</span><span style="color:#ba2121">"<br>"</span>;
</span></span><span style="display:flex;"><span> }
</span></span><span style="display:flex;"><span>}
</span></span><span style="display:flex;"><span>
</span></span><span style="display:flex;"><span><span style="color:#008000;font-weight:bold">function</span> <span style="color:#00f">greet</span>(){
</span></span><span style="display:flex;"><span><span style="color:#008000;font-weight:bold">print</span>(<span style="color:#ba2121">"<strong class="keylink">Go</strong>od Morning!"</span>)<span style="color:#666">.</span><span style="color:#ba2121">"<br>"</span>;
</span></span><span style="display:flex;"><span>}
</span></span><span style="display:flex;"><span>
</span></span><span style="display:flex;"><span><span style="color:#008000;font-weight:bold">const</span> <span style="color:#800">greeting</span> <span style="color:#666">=</span> <span style="color:#ba2121">"have a nice day"</span><span style="color:#666">.</span><span style="color:#ba2121">"<br>"</span>;
</span></span></code></code>

<code>
<code class="php hljs" data-lang="php"><span style="display:flex;"><span><span style="color:#008000;font-weight:bold">require</span> <span style="color:#ba2121">'greetings.php'</span>;
</span></span><span style="display:flex;"><span><span style="color:#19177c">$hello</span> <span style="color:#666">=</span> <span style="color:#008000;font-weight:bold">new</span> subodh\project\Greetings;
</span></span><span style="display:flex;"><span>subodh\project\greet();
</span></span><span style="display:flex;"><span><span style="color:#008000;font-weight:bold">echo</span> subodh\project\greeting;
</span></span></code></code>

Output:

<code>
<code class="text hljs" data-lang="text"><span style="display:flex;"><span>Hello everyone!
</span></span><span style="display:flex;"><span>Good Morning!
</span></span><span style="display:flex;"><span>have a nice day
</span></span></code></code>

---

Implement use and namespace

in PHP

We can use the use keyword in PHP to import the namespace in PHP and give it an alias. Therefore, we can replace long namespaces with short aliases.

This improves code readability. We can use aliases to represent namespaces.

First, we will use the use keyword to create an alias for the namespace of the example code written above.

For example, in the index.php file, write the use keyword, and import the namespace written in the greetings.php file as use subodh\project.

This means that now we can use project to access classes, functions and constants as shown in the example below.

<code>
<code class="php hljs" data-lang="php"><span style="display:flex;"><span><span style="color:#008000;font-weight:bold">require</span> <span style="color:#ba2121">'greetings.php'</span>;
</span></span><span style="display:flex;"><span><span style="color:#008000;font-weight:bold">use</span> subodh\project;
</span></span><span style="display:flex;"><span>
</span></span><span style="display:flex;"><span><span style="color:#19177c">$hello</span> <span style="color:#666">=</span> <span style="color:#008000;font-weight:bold">new</span> project\Greetings;
</span></span><span style="display:flex;"><span>project\greet();
</span></span><span style="display:flex;"><span><span style="color:#008000;font-weight:bold">echo</span> project\greeting;
</span></span></code></code>

We can also create custom aliases as follows.

<code>
<code class="php hljs" data-lang="php"><span style="display:flex;"><span><span style="color:#008000;font-weight:bold">require</span> <span style="color:#ba2121">'greetings.php'</span>;
</span></span><span style="display:flex;"><span>
</span></span><span style="display:flex;"><span><span style="color:#008000;font-weight:bold">use</span> subodh\project <span style="color:#008000;font-weight:bold">as</span> pr;
</span></span><span style="display:flex;"><span>
</span></span><span style="display:flex;"><span><span style="color:#19177c">$hello</span> <span style="color:#666">=</span> <span style="color:#008000;font-weight:bold">new</span> pr\Greetings;
</span></span><span style="display:flex;"><span>pr\greet();
</span></span><span style="display:flex;"><span><span style="color:#008000;font-weight:bold">echo</span> pr\greeting;
</span></span></code></code>

We can also import classes, functions and constants using the use keyword. We can write the namespace after the use keyword of the class.

First, we should append the class name at the end of the namespace. We can then access the class directly.

In case of functions and constants, we should write keywords function and constant respectively after use keyword.

After that, we can write the namespace, names of additional functions and constants. An example is shown below.

<code>
<code class="php hljs" data-lang="php"><span style="display:flex;"><span><span style="color:#008000;font-weight:bold">use</span> subodh\project\Greetings;
</span></span><span style="display:flex;"><span><span style="color:#19177c">$hello</span> <span style="color:#666">=</span> <span style="color:#008000;font-weight:bold">new</span> Greetings;
</span></span><span style="display:flex;"><span>
</span></span><span style="display:flex;"><span><span style="color:#008000;font-weight:bold">use</span> <span style="color:#008000;font-weight:bold">function</span> <span style="color:#00f">subodh\project\greet</span>;
</span></span><span style="display:flex;"><span>greet();
</span></span><span style="display:flex;"><span>
</span></span><span style="display:flex;"><span><span style="color:#008000;font-weight:bold">use</span> <span style="color:#008000;font-weight:bold">const</span> <span style="color:#800">subodh\project\greeting</span>;
</span></span><span style="display:flex;"><span><span style="color:#008000;font-weight:bold">echo</span> greeting;
</span></span></code></code>

The output of all the above methods is the same.

Output:

<code>
<code class="text hljs" data-lang="text"><span style="display:flex;"><span>Hello everyone!
</span></span><span style="display:flex;"><span>Good Morning!
</span></span><span style="display:flex;"><span>have a nice day
</span></span></code></code>

---

Grouping multiple classes using use in PHP

As introduced in PHP7, we can group classes, functions and constants when using the use keyword.

This feature prevents multiple uses of the use keyword and makes code cleaner and easier to read.

The number of lines of code is also reduced and reusability is maintained. Let us consider the following vehicle.php file.

It contains two classes, Car and Motorcycle, and constructors. Additionally, we created the namespace subodh\project.

<code>
<code class="php hljs" data-lang="php"><span style="display:flex;"><span><span style="color:#008000;font-weight:bold">namespace</span> subodh\project;
</span></span><span style="display:flex;"><span>
</span></span><span style="display:flex;"><span><span style="color:#008000;font-weight:bold">class</span> <span style="color:#00f;font-weight:bold">Car</span>{
</span></span><span style="display:flex;"><span><span style="color:#008000;font-weight:bold">public</span> <span style="color:#008000;font-weight:bold">function</span> __construct(){
</span></span><span style="display:flex;"><span><span style="color:#008000;font-weight:bold">print</span>(<span style="color:#ba2121">"This is Car class"</span>)<span style="color:#666">.</span><span style="color:#ba2121">"<br>"</span>;
</span></span><span style="display:flex;"><span> }
</span></span><span style="display:flex;"><span>}
</span></span><span style="display:flex;"><span>
</span></span><span style="display:flex;"><span><span style="color:#008000;font-weight:bold">class</span> <span style="color:#00f;font-weight:bold">Motorcycle</span>{
</span></span><span style="display:flex;"><span><span style="color:#008000;font-weight:bold">public</span> <span style="color:#008000;font-weight:bold">function</span> __construct(){
</span></span><span style="display:flex;"><span><span style="color:#008000;font-weight:bold">print</span>(<span style="color:#ba2121">"This is Motorcycle class"</span>)<span style="color:#666">.</span><span style="color:#ba2121">"<br>"</span>;
</span></span><span style="display:flex;"><span> }
</span></span><span style="display:flex;"><span>}
</span></span></code></code>

We can import both classes as the same namespace using the use keyword once. We can include the class name in curly braces after the namespace.

We can even create an alias for this class. Commas separate class names.

例如，在 use 关键字之后写入命名空间 subodh\project\{}。然后，在花括号内，写上 Car 类，并在逗号后写摩托车类。

最后，为 Motorcycle 类写别名 bike。现在，我们可以通过使用 new 关键字实例化 Car 和 bike 来创建这些类的对象。

<code>
<code class="php hljs" data-lang="php"><span style="display:flex;"><span><span style="color:#008000;font-weight:bold">require</span>(<span style="color:#ba2121">'vehicle.php'</span>);
</span></span><span style="display:flex;"><span><span style="color:#008000;font-weight:bold">use</span> subodh\project\{Car, Motorcycle <span style="color:#008000;font-weight:bold">as</span> bike};
</span></span><span style="display:flex;"><span><span style="color:#19177c">$car</span> <span style="color:#666">=</span> <span style="color:#008000;font-weight:bold">new</span> Car;
</span></span><span style="display:flex;"><span><span style="color:#19177c">$bike</span> <span style="color:#666">=</span> <span style="color:#008000;font-weight:bold">new</span> bike;
</span></span></code></code>

输出：

<code>
<code class="text hljs" data-lang="text"><span style="display:flex;"><span>This is Car class
</span></span><span style="display:flex;"><span>This is Motorcycle class
</span></span></code></code>

因此，我们可以使用 use 关键字对 PHP 命名空间中的类进行分组。我们也可以类似地对函数和常量进行分组。

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