Implemented by objects that hold a value.

@param <V> value type

abstract class TakesValue<V> {

 /**
  * Sets the value.
  * Fires [ValueChangeEvent] when
  * fireEvents is true and the new value does not equal the existing value.
  *
  * @param value a value object of type V
  * @see #getValue()
  * @param fireEvents fire events if true and value is new
  */
 void setValue(V val, [bool fireEvents = false]);

 /**
  * Returns the current value.
  *
  * @return the value as an object of type V
  * @see #setValue
  */
 V getValue();
}