(Hacky) DCI in PHP 5.4, version 2

dci2.php

<?php
//SEE ALSO: https://gist.github.com/mbrowne/5562643  (works in PHP 5.3 too)
//and related discussion: https://groups.google.com/d/msg/object-composition/g4BMSdluuC8/yPR3-a1b2sMJ

ini_set('display_errors', 1);

trait AssignableToRole
{
    protected $roles = array();
    protected $methods = array();
    protected $currentRole;
    
    public function addRole($traitOrClassName) {
    	if (trait_exists($traitOrClassName)) {
    		$className = $traitOrClassName.'Class';
    		//We need a real class in order to be able to instantiate it,
    		//so we can pass the instance to getClosure() below
    		if (!class_exists($className)) {
    			eval('class '.$className.' {use '.$traitOrClassName.';}');
    		}
    	}
    	else {
    		$this->checkRoleDefined($traitOrClassName);
    		$className = $traitOrClassName;
    	}
    	
    	//copy the methods from the role class
	$tmp = new $className;
	$reflClass = new ReflectionClass($tmp);
	$reflMethods = $reflClass->getMethods();
	foreach ($reflMethods as $method) {
		$this->addMethod($traitOrClassName, $method->name, $method->getClosure($tmp));
	}
  	return $this;
    }
    
    protected function addMethod($roleName, $methodName, $methodCallable)
    {
        if (!is_callable($methodCallable)) {
            throw new InvalidArgumentException('The $methodCallable parameter must be callable');
        }
        $this->methods[$methodName][$roleName] = Closure::bind($methodCallable, $this, get_class());
        $this->roles[$roleName]['methodNames'][] = $methodName;
    }
    
    public function asRole($traitOrClassName) {
    	$this->checkRoleDefined($traitOrClassName);
    	$this->checkRoleAssigned($traitOrClassName);
    	$this->currentRole = $traitOrClassName;
    	return $this;
    }
    
    public function removeRole($traitOrClassName) {
	$this->checkRoleDefined($traitOrClassName);
	try {
		$this->checkRoleAssigned($traitOrClassName);
		foreach ($this->roles[$traitOrClassName]['methodNames'] as $methodName) {
			unset($this->methods[$methodName][$traitOrClassName]);
		}
		unset($this->roles[$traitOrClassName]);
	}
	catch (InvalidArgumentException $e) {
		trigger_error($e->getMessage(), E_USER_NOTICE);
	}
	return $this;
    }
    
    protected function checkRoleDefined($traitOrClassName) {
    	if (!trait_exists($traitOrClassName) && !class_exists($traitOrClassName.'Class')) {
    		throw new InvalidArgumentException("Trait or class named '$traitOrClassName' is not defined");
    	}
    }
    
    protected function checkRoleAssigned($traitOrClassName) {
    	if (!array_key_exists($traitOrClassName, $this->roles)) {
    		throw new InvalidArgumentException("Trait or class named '$traitOrClassName' is not currently assigned to this instance");
    	}
    }
 
    public function __call($methodName, array $args)
    {
        if (isset($this->methods[$methodName])) {
        	if ($this->currentRole) {
			$ret = call_user_func_array($this->methods[$methodName][$this->currentRole], $args);
			$this->currentRole = null;
			return $ret;
        	}
        	else {
			$methods = $this->methods[$methodName];
			if (count($methods) > 1) {
				throw new RuntimeException(
					"There is more than one role with the method '$methodName' currently assigned to this object.
					Use the asRole() method to specify which role to use."
				);
			}
			$method = current($methods);
			call_user_func_array($method, $args);
        	}   
            
        }
        else throw new RuntimeException("There is no method named '$methodName' to call");
    }
}

class Person
{
	use AssignableToRole;
}

trait EmployeeRole
{
	function work() {
		echo "I'm working on it...";
	}
	
	function goofOff() {
		echo "Goofing off now even though I should be doing my job :)";
	}
}

trait StudentRole
{
	function goofOff() {
		echo "Goofing off now even though I should be studying :)";
	}
}

$person = new Person;
$person->addRole('EmployeeRole');
$person->addRole('StudentRole');

$person->work();
$person->asRole('EmployeeRole')->goofOff();
$person->asRole('StudentRole')->goofOff();

$person->removeRole('StudentRole');
//$person->asRole('StudentRole')->goofOff(); //would throw an exception