silverstripe-framework/tests/php/Core/ObjectTest/Extending.php

<?php

namespace SilverStripe\Core\Tests\ObjectTest;

use SilverStripe\Core\Object;
use SilverStripe\Dev\TestOnly;

class Extending extends Object implements TestOnly
{

	private static $extensions = array(
		Extending_Extension::class,
	);

	public function getResults(&$first, &$second, &$third)
	{
		// Before extending should be invoked second
		$this->beforeExtending('updateResult', function (&$first, &$second, &$third) {
			if ($first === 1 && $second === 2 && $third === 3) {
				$first = 11;
				$second = 12;
				$third = 13;
				return 'before';
			}
			return 'before-error';
		});

		// After extending should be invoked fourth
		$this->afterExtending('updateResult', function (&$first, &$second, &$third) {
			if ($first === 21 && $second === 22 && $third = 23) {
				$first = 31;
				$second = 32;
				$third = 33;
				return 'after';
			}
			return 'after-error';
		});

		// Function body invoked first
		$result = $this->extend('updateResult', $first, $second, $third);
		return array($result);
	}
}