Namespaces

Namespaces are a common idea in many programming languages and 0:00 PHP has had them since PHP 5.3. 0:03 To some developers, they still feel a little new. 0:05 So let's take a look at how they work. 0:08 The basic idea of using namespaces is to ensure that two difference classes, 0:10 functions, or constants with the same name do not cause conflicts. 0:14 For example, if you try to define two classes called client, 0:17 then the second definition will cause a fatal error, 0:21 complaining that you can not redefine that class. 0:23 If instead, you put that class into a namespace, 0:25 you can refer to both of them differently. 0:28 Let's take a look at how that works with some code. 0:30 Before we get started, pay no attention to line four, 0:33 as I'll explain about display errors later on. 0:35 So on line seven, we're including a third-party piece of 0:38 code that has been placed in the source folder which handles HTTP interactions. 0:41 On line eight, we're including another third-party piece of 0:46 code which will help us interact with the Twitter API. 0:48 Sadly, the developer of both the HTTP code and the Twitter code has not 0:52 used namespaces and instead declared the classes into global namespace. 0:56 Now we have these two client classes which looks a little funny and 1:00 will throw an error when we try and run the preview. 1:03 So you can see here, they've had trouble redeclaring the class client 1:05 because there's already a class called client. 1:10 If we have a look at the code we can see how to fix this. 1:12 We go into the source folder and inside the HTTP folder and look at the Client. 1:16 You can see here that there's no namespace declaration. 1:21 Now our namespace declaration is simply the word namespace and then the name. 1:23 We save that and we do the same thing to Twitter and save that too. 1:30 Now when we run this, PHP gives us a different error. 1:36 The complaint here is the class client does not exist. 1:39 Which is completely true. 1:41 Now the class client is not being defined in the global space. 1:43 It has to be referenced with the namespace. 1:46 Let's get back to our workspace and try that out. 1:48 So if we remember the names of our namespaces, which were HTTP, 1:52 we type that in and we use a backslash to de-reference it. 1:55 Do the same for Twitter, and now we've referenced our two different client 2:00 classes correctly with their namespaces so PHP knows where to find that code. 2:03 We run this again. 2:07 We can see that two objects, HTTPClient and TwitterClient, have been created. 2:10 We can further improve this code by using auto-loading, and 2:14 that's what we'll do in the next lesson. 2:17