Macro guion::impl_traitcast_mut

macro_rules! impl_traitcast_mut {
    ($( $trait:ty => |$id:pat| $access:expr; )*) => { ... };
}

This macro is used inside WidgetMut impls

Example: impl_traitcast_mut!( dyn IButton => |s| s; dyn IButtonState => |s| &mut s.state; );