WordPress – Fatal error: Call to a member function when calling class

I have created a php class in my theme function.php

class myWidgetSetting {

    function get_title(){
     //some blah blah code
    }

}

$setting = new myWidgetSetting();

but when I call this class $setting->get_title() inside:

class myWidget extends WP_Widget {
    $setting->get_title();
}

Then I get this error:

Fatal error: Call to a member function get_title() on a non-object in D:\wamp\www\wp-content\themes\twentyten\widgets\myWidget.php on line 3

Do i need to register class to wordpress ??

NOTE: Both class are in same file