namespace Test;
use Symfony\Component\PropertyAccess\PropertyAccess;

class Bar {
    private $foo;

    public function setFoo($foo) {
        $this->foo = $foo;
    }

    public function getFoo() {
        return $this->foo;
    }
}

class A {
    private $bars;

    public function __construct() {
        $this->bars = array(
            'a' => new Bar(),
            'b' => new Bar(),
        );
    }

    public function getBars() {
        return $this->bars;
    }
}

class MyTest extends \PHPUnit_Framework_TestCase {

    public function testPropertyAccessor() {
        $accessor = PropertyAccess::createPropertyAccessor();

        $a = new A();

        $accessor->setValue($a, 'bars[a].foo', 'baz');

        $this->assertEquals('baz', $a->getBars()['a']->getFoo());
    }
}