Macro stores 

macro_rules! stores {
    (
        $(#[$attr:meta])*
        $vis:vis struct $name:ident {
            $( $field:ident : $kind:ident < $row:ty > ),* $(,)?
        }
    ) => { ... };
}

Declares the store struct and implements Stores; its snapshot type is <A as Stores>::Snapshot.