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PHP Namespaces What Are They?

In PHP version 5.3 a new feature known as namespacing was added to the language. Many modern languages already had this feature for some time, but PHP was a little late to the scene. None the less, every new feature has a purpose, let’s find out why PHP namespaces can benefit our application.

In PHP you can’t have two classes that share the same name. They have to be unique. The issue with this restriction is that if you are using a third party library which has a class named User, then you can’t create your own class also called User. This is a real shame, because that’s a pretty convenient class name right?

PHP namespaces allow us to circumvent this issue, in fact we can have as many User classes as we like. Not only that, but we can use namespaces to contain our similar code into neat little packages, or even to show ownership.

Global Namespacing

There’s nothing special to it, if we want to use it then we can do this.

Basically, we can think of this class as being in the ‘global’ namespace. I don’t know if that’s the right term for it, but it sounds quite fitting to me. It essentially means that the class exists without a namespace. It’s just a normal class.

Simple Namespacing

Let’s create another class alongside the original, global Eddard.

Here we have another Eddard class, with one minor change. The addition of the namespace directive. The line namespace Stark; informs PHP that everything we do is relative to the Stark namespace. It also means that any classes created within this file will live inside the ‘Stark’ namespace.

Now, when we try to use the ‘Stark’ class once again.

Once again, we get an instance of the first class we created in the last section. Not the one within the ‘Stark’ namespace. Let’s try to create an instance of the ‘Eddard’ within the ‘Stark’ namespace.

We can instantiate a class within a namespace, by prefixing it with the name of the namespace, and separating the two with a backward (\) slash. Now we have an instance of the ‘Eddard’ class within the ‘Stark’ namespace. Aren’t we magical?!

You should know that namespaces can have as many levels of hierarchy as they need to. For example:

By adding the namespace directive to the instantiation example, we have moved the execution of the PHP script into the ‘Stark’ namespace. Now because we are inside the same namespace as the one we put ‘Eddard’ into, this time we receive the namespaced ‘Eddard’ class. See how it’s all relative?

Now that we have changed namespace, we have created a little problem. Can you guess what it is? How do we instantiate the original ‘Eddard’ class? The one not in the namespace.

Fortunately, PHP has a trick for referring to classes that are located within the global namespace, we simply prefix them with a backward (\) slash.

With the leading backward (\) slash, PHP knows that we are referring to the ‘Eddard’ in the global namespace, and instantiates that one.

Imagine that we have another namespaced class called Tully\Edmure. Now we want to use this class from within the ‘Stark’ framework. How do we do that?

Again, we need the prefixing backward slash to bring us back to the global namespace, before instantiating a class from the ‘Tully’ namespace.

It could get tiring, referring to classes within other namespaces by their full hierarchy each time. Luckily, there’s a nice little shortcut we can use. Let’s see it in action.

Using the use statement, we can bring one class from another namespace, into the current namespace. Allowing us to instantiate it by name only. Now don’t ask me why it doesn’t need the backward slash prefix, because I just don’t know. This is the only exception that I know of. Sorry about that! You can prefix it with a slash if you want to though, you just don’t need to.

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