wikimedia / mediawiki

includes/libs/ObjectFactory.php

<?php
/**
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 * http://www.gnu.org/copyleft/gpl.html
 *
 * @file
 */

/**
 * Construct objects from configuration instructions.
 *
 * @author Bryan Davis <bd808@wikimedia.org>
 * @copyright © 2014 Bryan Davis and Wikimedia Foundation.
 */
class ObjectFactory {

	/**
	 * Instantiate an object based on a specification array.
	 *
	 * The specification array must contain a 'class' key with string value
	 * that specifies the class name to instantiate or a 'factory' key with
	 * a callable (is_callable() === true). It can optionally contain
	 * an 'args' key that provides arguments to pass to the
	 * constructor/callable.
	 *
	 * Values in the arguments collection which are Closure instances will be
	 * expanded by invoking them with no arguments before passing the
	 * resulting value on to the constructor/callable. This can be used to
	 * pass IDatabase instances or other live objects to the
	 * constructor/callable. This behavior can be suppressed by adding
	 * closure_expansion => false to the specification.
	 *
	 * The specification may also contain a 'calls' key that describes method
	 * calls to make on the newly created object before returning it. This
	 * pattern is often known as "setter injection". The value of this key is
	 * expected to be an associative array with method names as keys and
	 * argument lists as values. The argument list will be expanded (or not)
	 * in the same way as the 'args' key for the main object.
	 *
	 * @param array $spec Object specification
	 * @return object
	 * @throws InvalidArgumentException when object specification does not
	 * contain 'class' or 'factory' keys
	 * @throws ReflectionException when 'args' are supplied and 'class'
	 * constructor is non-public or non-existent
	 */
	public static function getObjectFromSpec( $spec ) {
		$args = isset( $spec['args'] ) ? $spec['args'] : [];
		$expandArgs = !isset( $spec['closure_expansion'] ) ||
			$spec['closure_expansion'] === true;

		if ( $expandArgs ) {
			$args = static::expandClosures( $args );
		}

		if ( isset( $spec['class'] ) ) {
			$clazz = $spec['class'];
			if ( !$args ) {
				$obj = new $clazz();
			} else {
				$obj = static::constructClassInstance( $clazz, $args );
			}
		} elseif ( isset( $spec['factory'] ) ) {
			$obj = call_user_func_array( $spec['factory'], $args );
		} else {
			throw new InvalidArgumentException(
				'Provided specification lacks both factory and class parameters.'
			);
		}

		if ( isset( $spec['calls'] ) && is_array( $spec['calls'] ) ) {
			// Call additional methods on the newly created object
			foreach ( $spec['calls'] as $method => $margs ) {
				if ( $expandArgs ) {
					$margs = static::expandClosures( $margs );
				}
				call_user_func_array( [ $obj, $method ], $margs );
			}
		}

		return $obj;
	}

	/**
	 * Iterate a list and call any closures it contains.
	 *
	 * @param array $list List of things
	 * @return array List with any Closures replaced with their output
	 */
	protected static function expandClosures( $list ) {
		return array_map( function ( $value ) {
			if ( is_object( $value ) && $value instanceof Closure ) {
				// If $value is a Closure, call it.
				return $value();
			} else {
				return $value;
			}
		}, $list );
	}

	/**
	 * Construct an instance of the given class using the given arguments.
	 *
	 * PHP's `call_user_func_array()` doesn't work with object construction so
	 * we have to use other measures. Starting with PHP 5.6.0 we could use the
	 * "splat" operator (`...`) to unpack the array into an argument list.
	 * Sadly there is no way to conditionally include a syntax construct like
	 * a new operator in a way that allows older versions of PHP to still
	 * parse the file. Instead, we will try a loop unrolling technique that
	 * works for 0-10 arguments. If we are passed 11 or more arguments we will
	 * take the performance penalty of using
	 * `ReflectionClass::newInstanceArgs()` to construct the desired object.
	 *
	 * @param string $clazz Class name
	 * @param array $args Constructor arguments
	 * @return mixed Constructed instance
	 */
	public static function constructClassInstance( $clazz, $args ) {
		// $args should be a non-associative array; show nice error if that's not the case
		if ( $args && array_keys( $args ) !== range( 0, count( $args ) - 1 ) ) {
			throw new InvalidArgumentException( __METHOD__ . ': $args cannot be an associative array' );
		}

		// TODO: when PHP min version supported is >=5.6.0 replace this
		// with `return new $clazz( ... $args );`.
		$obj = null;

$obj is not used, you could remove the assignment.

		switch ( count( $args ) ) {
			case 0:
				$obj = new $clazz();
				break;
			case 1:
				$obj = new $clazz( $args[0] );
				break;
			case 2:
				$obj = new $clazz( $args[0], $args[1] );
				break;
			case 3:
				$obj = new $clazz( $args[0], $args[1], $args[2] );
				break;
			case 4:
				$obj = new $clazz( $args[0], $args[1], $args[2], $args[3] );
				break;
			case 5:
				$obj = new $clazz(
					$args[0], $args[1], $args[2], $args[3], $args[4]
				);
				break;
			case 6:
				$obj = new $clazz(
					$args[0], $args[1], $args[2], $args[3], $args[4],
					$args[5]
				);
				break;
			case 7:
				$obj = new $clazz(
					$args[0], $args[1], $args[2], $args[3], $args[4],
					$args[5], $args[6]
				);
				break;
			case 8:
				$obj = new $clazz(
					$args[0], $args[1], $args[2], $args[3], $args[4],
					$args[5], $args[6], $args[7]
				);
				break;
			case 9:
				$obj = new $clazz(
					$args[0], $args[1], $args[2], $args[3], $args[4],
					$args[5], $args[6], $args[7], $args[8]
				);
				break;
			case 10:
				$obj = new $clazz(
					$args[0], $args[1], $args[2], $args[3], $args[4],
					$args[5], $args[6], $args[7], $args[8], $args[9]
				);
				break;
			default:
				// Fall back to using ReflectionClass and curse the developer
				// who decided that 11+ args was a reasonable method
				// signature.
				$ref = new ReflectionClass( $clazz );
				$obj = $ref->newInstanceArgs( $args );
		}
		return $obj;
	}
}