Separate declarations from side-effects about underpin HOT 6 CLOSED

<?php
/**
 * Autoloader for WordPress.
 *
 * @package Underpin
 * @link https://make.wordpress.org/core/handbook/best-practices/coding-standards/php/#naming-conventions
 * @link https://github.com/php-fig/fig-standards/blob/master/accepted/PSR-4-autoloader-examples.md#class-example
 */

declare( strict_types = 1 );

namespace Underpin;

use function spl_autoload_register;

spl_autoload_register(
	/**
	 * Closure of the autoloader.
	 *
	 * @param class-string $class_name The fully-qualified class name.
	 * @return void
	 */
	static function ( $class_name ) {
		$project_namespace = __NAMESPACE__ . '\\';
		$length            = strlen( $project_namespace );

		// Class is not in our namespace.
		if ( 0 !== strncmp( $project_namespace, $class_name, $length ) ) {
			return;
		}

		// E.g. Model\Item
		$relative_class_name = substr( $class_name, $length );
		// E.g. model/Item.php
		$name_parts = explode( '\\', $relative_class_name );
		$last_part  = array_pop( $name_parts );

		$file = sprintf(
			'%1$s/lib%2$s/%3$s.php',
			__DIR__,
			array() === $name_parts ? '' : '/' . strtolower( str_replace( '_', '-', implode( '/', $name_parts ) ) ),
			$last_part
		);

		if ( ! is_file( $file ) ) {
			return;
		}

		require $file;
	}
);