Determines if a given method name can be responded to. Classes with magic methods should extend the method. Originally, I was going to have the default `$visibility` to null and auto-detect if it was an internal class or not, but that turned out to be rather slow. (https://gist.github.com/4658402)

respondsTo.php

<?php

namespace foo\bar\baz;

use ReflectionClass;
use ReflectionMethod;
use Exception;
use BadMethodCallException;

error_reporting(-1);

class foo {

	/**
	 * Will determine if a method can be called.
	 *
	 * @param  string  $method     Method name.
	 * @param  integer $visibility Visibility (1 for public, 2 for public and
	 *              protected, and 3 for all visibility)
	 * @return bool
	 */
	public function respondsTo($method, $visibility = 0) {
		$class = new ReflectionClass($this);
		$types = array();
		$types[0] = ReflectionMethod::IS_PUBLIC;
		$types[1] = $types[0] | ReflectionMethod::IS_PROTECTED;
		$types[2] = $types[1] | ReflectionMethod::IS_PRIVATE;
		foreach ($class->getMethods($types[$visibility]) as $reflectMethod) {
			if ($reflectMethod->getName() === $method) {
				return true;
			}
		}
		return false;
	}

	public function foo() {
		return;
	}

	protected function foobaz() {
		return;
	}

}

class foobar extends foo {

	protected $_magicMethods = array();

	public function __construct() {
		$this->_magicMethods = array(
			'bar' => function() {
				return;
			},
			'baz' => function() {
				return;
			}
		);
	}

	public function __call($method, $args) {
		if (in_array($method, $this->_magicMethods, 1)) {
			return $this->foo();;
		}
		throw new BadMethodCallException;
	}

	/**
	 * Custom check to determine if our given magic methods can be responded to.
	 *
	 * @param  string  $method     Method name.
	 * @param  integer $visibility Visibility (1 for public, 2 for public and
	 *              protected, and 3 for all visibility)
	 * @return bool
	 */
	public function respondsTo($method, $visibility = 0) {
		return isset($this->_magicMethods[$method]) || parent::respondsTo($method, $visibility);
	}

}

$foobar = new foobar();
var_dump(
	$foobar->respondsTo('foo'), // true
	$foobar->respondsTo('bar'), // true
	$foobar->respondsTo('baz'), // true
	$foobar->respondsTo('foobaz'), // false
	$foobar->respondsTo('foobaz', 1) // true
);

It might be faster to do ReflectionClass::getMethod instead and do visibility checks after, but I'll benchmark before submitting a pr if this is desired functionality.