Derive Macro Reactive 

#[derive(Reactive)]
{
    // Attributes available to this derive:
    #[reactive]
    #[var]
    #[computed]
}

Derive macro for the reactive field system.

Annotate struct fields with #[reactive], #[reactive(layout)], #[reactive(watch)], or #[var] to generate getters, setters with change detection, and watcher dispatch.