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;
);