PHP
Using with file inclusion
Move the class to a separate file and use it in another page with include.
Moving the class to its own file
If you want to reuse a class across projects, it's best to move it into its own file: Collection.php. The class definition is then separated from where it's used, keeping code organized.
In this lesson you'll load the class code into a variable, write it to a file with file_put_contents, then include it with require_once and use it. This mirrors creating the class file by hand in a real project.
Safe paths with __DIR__
Writing a relative path when including a file is risky; the path breaks if the script runs from a different directory. The __DIR__ magic constant returns the absolute path of the file's directory.
With __DIR__ . "/Collection.php" the path stays correct no matter where you run from. You write the class with file_put_contents and load it with require_once.
Exercise Write the class to a file and use it with require_once
Build the file path with $classFile = __DIR__ . "/Collection.php";. Write the class code to the file with file_put_contents($classFile, $classCode);. Include it with require_once $classFile;. Then start with $c = new Collection(["apple"]);, chain $c->add("pear")->add("cherry"); and print the count with echo count($c->items);.
Show example solution
Set $classFile = __DIR__ . "/Collection.php";. Write file_put_contents($classFile, $classCode);. Add require_once $classFile;. Start with new Collection(["apple"]), chain $c->add("pear")->add("cherry");.
Example solution:
<?php
// Write the Collection class to a separate file, then load it with require_once here
$classCode = '<?php
class Collection {
public array $items = [];
public function __construct(array $initial = []) {
$this->items = $initial;
}
public function add(string $item) {
$this->items[] = $item;
return $this;
}
}';
$classFile = __DIR__ . "/Collection.php";
file_put_contents($classFile, $classCode);
require_once $classFile;
$c = new Collection(["apple"]);
$c->add("pear")->add("cherry");
echo count($c->items);
Test yourself
-
Best statement to safely include a class file?
- include
- include_once
- require
- require_once
Show answer
require_once — Correct. require_once includes the class file once; it gives a fatal error if missing and prevents duplicate definitions.
-
Include Collection.php with require_once
require_once ____;
Show answer
require_once __DIR__ . "/Collection.php";
-
Match the file inclusion concepts
- require_once
- Includes once, fatal if missing
- require
- Includes each time, fatal if missing
- include
- Warns, script continues
- __DIR__
- File's directory
Next lesson: Project final - Library
