In the previous tutorial, we covered a handful of concepts, all of which are going to be necessary to fully understand what we're doing in this tutorial.
Specifically, we covered the following topics:
In some series, it's easy to skip tutorials that may not build on one another; however, this series isn't intended to be like that. Instead, it's meant to be read in sequential order, and it's meant to build on the content of each previous tutorial.
With that said, I'm assuming you're all caught up.
Even though I might have mentioned this in the first tutorial, I still like to make sure we're all on the same page with regard to what we're doing in each tutorial and with what software you're going to need.
So in this tutorial, the plan is as follows:
Ultimately, we won't be writing much code in this tutorial, but we'll be writing some. It is, however, a practical tutorial in that we're performing object-oriented analysis and design. This is a necessary phase for many large-scale projects (and something that should happen for small-scale projects).
If you've been following along, you should have this already set up. But to make sure, here's the short version of everything you need:
With all of that in place, we're ready to work on the code shared in the previous tutorial. So let's get started.
The very first thing we want to do is analyze the current state of our autoloader. It might seem like a lot of code to paste into a single block of code, but that in and of itself shows us that we have some work to do.
With that said, here's the current state of our autoloader:
<?php function tutsplus_namespace_demo_autoload( $class_name ) { // If the specified $class_name does not include our namespace, duck out. if ( false === strpos( $class_name, 'Tutsplus_Namespace_Demo' ) ) { return; } // Split the class name into an array to read the namespace and class. $file_parts = explode( '\\', $class_name ); // Do a reverse loop through $file_parts to build the path to the file. $namespace = ''; for ( $i = count( $file_parts ) - 1; $i > 0; $i-- ) { // Read the current component of the file part. $current = strtolower( $file_parts[ $i ] ); $current = str_ireplace( '_', '-', $current ); // If we're at the first entry, then we're at the filename. if ( count( $file_parts ) - 1 === $i ) { /* If 'interface' is contained in the parts of the file name, then * define the $file_name differently so that it's properly loaded. * Otherwise, just set the $file_name equal to that of the class * filename structure. */ if ( strpos( strtolower( $file_parts[ count( $file_parts ) - 1 ] ), 'interface' ) ) { // Grab the name of the interface from its qualified name. $interface_name = explode( '_', $file_parts[ count( $file_parts ) - 1 ] ); $interface_name = $interface_name[0]; $file_name = "interface-$interface_name.php"; } else { $file_name = "class-$current.php"; } } else { $namespace = '/' . $current . $namespace; } } // Now build a path to the file using mapping to the file location. $filepath = trailingslashit( dirname( dirname( __FILE__ ) ) . $namespace ); $filepath .= $file_name; // If the file exists in the specified path, then include it. if ( file_exists( $filepath ) ) { include_once( $filepath ); } else { wp_die( esc_html( "The file attempting to be loaded at $filepath does not exist." ) ); } }
At this point, remember that the single responsibility principle states the following:
A class should have only one reason to change.
Right now, we don't even have a class, let alone multiple individual methods that have only a single reason to change.
And though it might make sense to start by breaking this autoloader method into smaller, individual methods, let's start from a higher level and begin thinking about an autoloader in terms of an interface. Then we'll drill down into creating a class (or classes).
Recall from the previous tutorial that an interface is defined by the PHP manual as follows:
Object interfaces allow you to create code which specifies which methods a class must implement, without having to define how these methods are handled.
Given the code and the definitions above, let's think about what an autoloader needs to do from a more modular perspective. Specifically, let's break it down into points that represent what might be enough to change. No, we may not use all of these points, but this it's why it's called analysis. We'll work on the design later.
The code does the following:
$class_name
is a poor variable name).Thus, the above code does nine things—that is, it has at least nine reasons to change—before it's done completing its work.
This should go without saying, but this particular function is a perfect example that we can refactor to demonstrate object-oriented analysis, design, interfaces, and implementation.
And this raises a question: Where do we even begin?
At this point, it's fair to say that we can begin doing object-oriented analysis—that is, looking at what potential classes we may have and how they interact—given everything we've listed above. Remember, we also want the single responsibility principle to help guide us in our decision making.
At this point, we're not terribly concerned with how the classes will communicate with one another. Instead, we're more focused on creating classes that have a single reason to change.
With that said, I'm going to provide a sample set of classes that I think might work. Before going any further, look at what we've done and attempt to come up with your own list. Then we can compare notes.
Note that you may have a better idea than what's listed below, or you may take something away from what we've shared. Regardless, this is a learning exercise. We're attempting to improve our code, our organization, and ultimately become better programmers.
Given what I've listed above, I've come up with the following classes:
And that's it. Now third-party classes in our plugin only need to know about the autoloader class, but the autoloader will need knowledge of another class, and other classes will need knowledge of yet other classes.
There are ways to handle this (using dependency injection containers, but that's beyond the scope of this project). But what we'll aim to do through our code is minimize how many classes know about one another.
At this point, different developers, firms, agencies, and teams will take a different approach to how they design the system on which they are working.
One of the most common ways to go about doing this is to use something called a UML diagram. Though it's useful, it's not something that's worth doing within the scope of this tutorial because it will require a whole other tutorial to explain all of the pieces.
So for the purposes of our tutorial, and since we're working with such a small amount of code, we'll try to stub out how each of the above classes may work before we implement them. This way, we'll get an idea of how we can organize our code.
Note that we won't be namespacing any of this code just yet, and none of this code should be implemented or tested against WordPress just yet. We'll get into that in the next tutorial.
Let's start with the Autoloader
and work from there.
Remember, this class is responsible for including the necessary file. This is the file that will be registered with the spl_autoload_register
function.
<?php class Autoloader { private $namespace_validator; private $file_registry; public function __construct() { $this->namespace_validator = new NamespaceValidator(); $this->file_registry = new FileRegistry(); } public function load( $filename ) { if ( $this->namespace_validator->is_valid( $filename ) ) { $this->file_registry->load( $filename ); } } }
Note that this class depends on the NamespaceValidator
and the FileRegistry
class. We'll see each of these in more detail in just a moment.
This file will look at the incoming filename and will determine if it's valid. This is done by looking at the namespace in the filename.
<?php class NamespaceValidator { public function is_valid( $filename ) { return ( 0 === strpos( $filename, 'Tutsplus_Namespace_Demo' ) ); } }
If the file does in fact belong to our namespace, then we can assume it's safe to load our file.
This class is doing quite a bit of work, though part of it is done via very simple, very small helper methods. During the course of execution, it looks at the type of file that it's passed.
It then retrieves the fully-qualified filename for the type of file.
<?php class FileInvestigator { public function get_filetype( $filename ) { $filepath = ''; for ( $i = 1; $i < count( $file_parts ); $i++ ) { $current = strtolower( $file_parts[ $i ] ); $current = str_ireplace( '_', '-', $current ); $filepath = $this->get_file_name( $file_parts, $current, $i ); if ( count( $file_parts ) - 1 !== $i ) { $filepath = trailingslashit( $filepath ); } } return $filepath; } private function get_file_name( $file_parts, $current, $i ) { $filename = ''; if ( count( $file_parts ) - 1 === $i ) { if ( $this->is_interface( $file_parts ) ) { $filename = $this->get_interface_name( $file_parts ); } else { $filename = $this->get_class_name( $current ); } } else { $filename = $this->get_namespace_name( $current ); } return $filename; } private function is_interface( $file_parts ) { return strpos( strtolower( $file_parts[ count( $file_parts ) - 1 ] ), 'interface' ); } private function get_interface_name( $file_parts ) { $interface_name = explode( '_', $file_parts[ count( $file_parts ) - 1 ] ); $interface_name = $interface_name[0]; return "interface-$interface_name.php"; } private function get_class_name( $current ) { return "class-$current.php"; } private function get_namespace_name( $current ) { return '/' . $current; } }
If there's a file that can be refactored a bit more, then this is it. After all, it attempts to determine if we're working with a class, an interface, or a class. A simple factory might be better suited to this.
When it comes time to implement our code, perhaps we'll refactor this further. Until then, this is a preliminary design that may work well enough.
This will use the fully-qualified file path and include the file; otherwise, it will use the WordPress API to display an error message.
class FileRegistry { private $investigator; public function __construct() { $this->investigator = new FileInvestigator(); } public function load( $filepath ) { $filepath = $this->investigator->get_filetype( $filepath ); $filepath = rtrim( plugin_dir_path( dirname( __FILE__ ) ), '/' ) . $filepath; if ( file_exists( $filepath ) ) { include_once( $filepath ); } else { wp_die( esc_html( 'The specified file does not exist.' ) ); } } }
Another alternative to using the WordPress API would be to throw a custom Exception message. That way, we'd be able to completely separate or decouple our code from WordPress.
Once again, this code is a carry-over from the initial autoloader. During implementation, we may change this, as well.
Alright, so we've looked at the existing code for our autoloader, and then we've stubbed out some potential code that we can use based on some object-oriented analysis and design.
Is the solution that we're working toward more maintainable than what we have? Absolutely. Is this going to work within the context of WordPress and our existing plugin? We won't know until we begin to hook this up into our plugin.
As previously mentioned, there are still some areas in which we could possibly refactor this code. If we hit these type of issues when implementing our code in the final version of our plugin, we'll take a look at doing exactly that.
Whatever the case, the code that we have now should be more readable (though we still have DocBlocks and some inline comments to introduce) and more maintainable and even more testable.
With all of that said, I hope that this has given you an idea as to how to take a long method and break it into more purpose-driven classes. Sure, having multiple classes might feel weird at first, but that doesn't mean it's a bad thing. Have more files (and thus classes) with less code than one file with a lot of code is better.
Embrace the counterintuitive nature of object-oriented programming in this regard. In the next tutorial, we're going to be returning to our plugin and will be working on implementing a variation of the code above. We'll likely be debugging some of it as well. After all, rarely do we get it right the first time
Until then, if you're interested in reading more about object-oriented programming in the context of WordPress, you can find all of my previous tutorials on my profile page. Feel free to follow my on my blog or follow me on Twitter where I frequently talk about both.
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waly Good blog post. I absolutely love this…