PHP中优雅嵌套的类 - 任何建议？

I got a way to define nested classes in Php, but it is pretty raw.

class foo {

  function define_new_class($class, $code) {
    if (!class_exists($class)) {
      $definition = eval($code);
    }
  }

  function bar() {
    $new_class = "boo";
    $this->define_new_class($new_class, "class $new_class {}");
    $obj = new $new_class();

    echo "Current class: " . get_class($this) . "
"; // foo
    echo "\$obj class: " . get_class($obj) . "
"; // boo
  }
}

$foo = new foo();
$foo->bar();

Is it possible to do the same job in a gracefully way?

Since there is no way to define a true nested classes: instead of use a nested class you can create another class that starts with the name of OuterClass:

class OuterClass {
   ...stufs...
}
class OuterClass_InnerClass {
   ...stufs...
}

or use namespaces

class OuterClass {
   ...stufs...
}
class \OuterClass\InnerClass {
   ...stufs...
}