Macro downcast_trait::downcast_trait_mut

macro_rules! downcast_trait_mut {
    ( dyn $type:path, $src:expr) => { ... };
}

This macro can be used to cast a &dyn mut DowncastTrait to an implemented trait e.g:

if let Some(sub_container) =
    downcast_trait_mut!(dyn Container, sub_widget.as_ref().to_downcast_trait())
{
  //Use downcasted trait
}