Command invoker pattern

invoker.php

<?php
interface Command
{
	public static function register();

	public function execute();
}

class HelloCommand implements Command {
	protected $name;

	public static function register() {
		return function ($name) {
			return new HelloCommand($name);
		};
	}

	public function __construct($name) {
		$this->name = $name;
	}

	public function execute() {
		echo "Hello, " . $this->name . "\n";
	}
}

class PwdCommand implements Command {

	public static function register() {
		return function () {
			return new PwdCommand();
		};
	}

	public function execute() {
		echo "You are here: " . getcwd() . "\n";
	}
}

class CustomCommand implements Command {
	protected $foo;
	protected $bar;

	public static function register() {
		return function ($foo, $bar) {
			return new CustomCommand($foo, $bar);
		};
	}

	public function __construct($foo, $bar) {
		$this->foo = $foo;
		$this->bar = $bar;
	}

	public function execute() {
		echo "What does it all mean? " . ($this->foo + $this->bar) . "\n";
	}
}

class Invoker {
	protected $commandMap = array();

	public function __construct() {
		$this->register('hello', 'HelloCommand');
		$this->register('pwd', 'PwdCommand');
	}

	public function __call($command, $args) {
		if (!array_key_exists($command, $this->commandMap)) {
			throw new BadMethodCallException("$command is not a registered command");
		}
		$command = call_user_func_array($this->commandMap[$command], $args);
		$command->execute();
	}

	public function register($command, $commandClass) {
		if (!array_key_exists('Command', class_implements($commandClass))) {
			throw new LogicException("$commandClass does not implement the Command interface");
		}
		$this->commandMap[$command] = $commandClass::register();
	}
}

$invoker = new Invoker();
$invoker->hello('Josh');
$invoker->pwd();

$invoker->register('custom', 'CustomCommand');
$invoker->custom(40, 2);

$invoker->register('pwd', 'CustomCommand');
$invoker->pwd(2, 40);