Macro guion::impl_traitcast

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

This macro is used inside Widget/WidgetMut impls

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