olifilo

esp::idf::events

This implementation uses per-subscription IPC message queues to collect subscribed-to events. Notification of messages in these can be done by select() like other file descriptors via the VFS integration which delivers the event messages via its read() call.

The 'events::subscriber' class on top of that handles decoding into:

std::pair<std::variant<event_id_types...>, std::variant<event_payload_types...>>

For convenience:

1. All types in these variants are deduplicated
2. All event id types and payload types are sorted on tuple{sort_key_for(event_base), event_id}
3. void payloads are replaced by 'std::monostate'
   • which is sorted to the front
4. This pair will never contain variants with one (1) alternative only
   • they're replaced by that alternative in that case (without wrapping variant)
   • if, and only if, subscribing to exactly one event the return type is the associated payload type (without any wrapping pair & variants)
   • if the only payload type is void, and subscribing to more than 1 event, the pair is omitted and what would have been its first_type is returned instead.