Macro selfref_match 

macro_rules! selfref_match {
    (
        $selfref:expr, $field:ident {
            $( $first:ident $(:: $rest:ident)* ($binding:tt) => $body:block )*
        }
    ) => { ... };
}

Pattern-match on a field of a SelfRef<T>, projecting to SelfRef<VariantInner> in each arm body.

Uses Deref to peek at the discriminant without consuming, then .map() to project into the taken arm. The unreachable!() in each map closure is genuinely unreachable because the matches! guard ensures only the correct variant reaches it.

Variants not listed are silently consumed and dropped.

Example

selfref_match!(msg, payload {
    MessagePayload::RequestMessage(r) => { /* r: SelfRef<RequestMessage> */ }
    MessagePayload::ChannelMessage(c) => { /* c: SelfRef<ChannelMessage> */ }
})