switch($str) {
   case "One":
       return new ClassOne();
   case "Two":
       return new ClassTwo();
}

$str = "One";
$class = "Class".$str;
$object = new $class();

$personCount = 123;
$varname = 'personCount';
echo $$varname; // echo's 123

$func = 'my_function';
$func('param1'); // calls my_function('param1');

$method = 'doStuff';
$object = new MyClass();
$object->$method(); // calls the MyClass->doStuff() method.

$className = $whatever;
$object = new $className;

public function &factory($className) {

    require_once($className.'php');
    if(class_exists($className)) return new $className;

    die('Cannot create new "'.$className.'" class - includes not found or class unavailable.');
}

$className = 'Foo';
$instance = new $className(); // Foo()

public class ClassOne
{
    protected $arg1;
    protected $arg2;

    //Contructor
    public function __construct($arg1, $arg2)
    {
        $this->arg1 = $arg1;
        $this->arg2 = $arg2;
    }

    public function echoArgOne
    {
        echo $this->arg1;
    }

}

$str = "One";
$className = "Class".$str;
$class = new ReflectionClass($className);

$instance = $class->newInstanceArgs(["Banana", "Apple")]);

$instance->echoArgOne();
//prints "Banana"

$method = "echoArgOne";
$instance->$method();

//prints "Banana"