Autoloading

The require and require_once commands read in the file given as their argument regardless of whether the classes, functions, etc. are ever used.
In a web and interpreted environment this can result in slower performance, if there are a lot of files being included in this way.
On the other hand, a use declaration does not load anything into memory -- it is just declares a naming convention to be used for how to refer to classes and functions.
In PHP, we can use the spl_autoload_register($your_autoloader_function); command to register a PHP function to be called whether someone tries to instantiate a class or call a function which is not currently in memory.
Using autoloading, allows us to minimize the number of files we read in before executing code.
The autoloader function typically makes use of the namespace info from use declarations to search the file system to find the definition of the class or function that is being instantiated or used.

More Autoloading

To demonstrate autoloading, I'm going to discuss the Yioop search engine software that we've been using for the class discussion board...
The Yioop search engine can either make use of the autoloader that it comes with or it can use Composer's autoloader.

The code to check which to use and the native autoloader are in YIOOP_FOLDER/src/configs/Config.php. and looks like:

if (file_exists(__DIR__."/../../vendor/autoload.php")) {
    require_once __DIR__."/../../vendor/autoload.php";
} else {
    spl_autoload_register(function ($class) {
        // project-specific namespace prefix
        $prefix = 'seekquarry\\yioop\\tests';
        // does the class use the namespace prefix?
        $len = strlen($prefix);
        if (strncmp($prefix, $class, $len) !== 0) {
            $prefix = 'seekquarry\\yioop';
            $len = strlen($prefix);
            // no, move to the next registered autoloader
            if (strncmp($prefix, $class, $len) !== 0) {
                return;
            } else {
                $check_dirs = [WORK_DIRECTORY . "/app", BASE_DIR];
            }
        } else {
            $check_dirs = [PARENT_DIR . "/tests"];
        }
        // get the relative class name
        $relative_class = substr($class, $len);
        // use forward-slashes, add ./php
        $unixify_class_name = "/".str_replace('\\', '/', $relative_class) .
            '.php';
        foreach($check_dirs as $dir) {
            $file = $dir . $unixify_class_name;
            if (file_exists($file)) {
                require $file;
                break;
            }
        }
    });
}

Comments on the Yioop Autoloader

Notice the native autoloader gets a string name of the form some_namespace\class. The above autoloader checks if the namespace begins with seekquarry\yioop. If it doesn't then it returns -- it doesn't know how to autoload it.
Otherwise, we take the portion of the name after the vendor\project, $relative_class. For example, \seekquarry\yioop\models\Model, has $relative_class as \models\Model. We convert backslashes into forward slashes and tack on .php. Then we look to see if either of the files BASE_DIR . $relative_class or WORK_DIRECTORY . /app$relative_class exist and if so load it. I.e., in our example, we check for BASE_DIR . /model/Model.php and WORK_DIRECTORY/app/model/Model.php
For us to find the class we want, we need to follow the convention that a class is always defined in a file with the same name and in the appropriate relative folder.
The Composer project also follows this convention.

In-Class Exercise

Create a class some_company\some_project\IntHolder with a constructor which take an integer $a_num and stores in into a field variable $my_num.
In a separate file register an autoloader that looks for classes in the some_company\some_project namespace in the current directory and loads them if needed.

In the same file have a line:

use some_company\some_project\IntHolder ;

Then create an instance of IntHolder using the line and echo $my_num:

$int_holder = new IntHolder(6);
echo $int_holder->my_num ."\n";

Run your program to verify the autoloader is working.
Post your solutions (code plus test run) to the Apr 7 In-Class Exercise Thread.

Composer, PHP Traits, Version Control, Git

Outline

Autoloading

More Autoloading

Comments on the Yioop Autoloader

In-Class Exercise