During last Wednesday’s meeting, we agreed that it would be better to associate each object directly with its objectId type. This would let us avoid passing objectId object type parameters everywhere, and instead just pass object. It would also allow us to remove the oprObjectId and opwObjectId fields in ObjectPool{Reader,Writer}, which are essentially just getters for an object’s ID.

The idea would be to introduce a class:

class
  ( Ord (IdOf a)
  , Eq (IdOf a)
  , Show (IdOf a)
  , NoThunks (IdOf a)
  , Serialise (IdOf a)
  ) => HasId a where

  type IdOf a
  getId :: a -> IdOf a

and then provide instances such as HasId PerasCert, HasId PerasVote, etc.

NOTE: An alternative would be to use a multi-parameter type class with a functional dependency,
HasId object objectId | object -> objectId, but this would make it inconvenient to refer to the objectId type when defining a data type parameterised by object only.

The current concerns are:

1. Various ObjectDiffusion types are already parameterised by objectId object, including some in ouroboros-network. This means the change would need to span both repositories. As a result, we’d need to define HasId in ouroboros-network, or even higher up the dependency chain (e.g. in cardano-base).

2. We would need to enable FlexibleContexts and UndecidableInstances in some places. For example:

instance (Show objectId, Typeable object, Typeable objectId)
  => Exception (ObjectDiffusionInboundError objectId object)

would become:

instance (Show (IdOf object), Typeable object, Typeable (IdOf object))
  => Exception (ObjectDiffusionInboundError object)

and this seems to require those extensions.

Consequently, we’d like to get approval again from the IOG team before going down this route.
Whatever the final decision is, I think it would be best to continue with [Peras 4] as-is, and handle the objectId / HasId changes in a separate PR.

I changed the interface of ObjectPoolReader's method to oprObjectsAfter :: ticketNo -> Word64 -> STM m (Maybe (m (Map ticketNo object))) as we agreed last week, see b629e84 :)

Hi @IntersectMBO/ouroboros-consensus-maintainers , I've tried to addressed all required changes that we discussed last week, see commits bf4767a .. 5674b30. Let me know if anything still needs to be adjusted.

I'll squash these fixup commits once you've had time to look at them :)

Ok, now the last small issue on smoke tests has been fixed, so this is ready :)

I just squashed the fixup commits, and rebased on top of main, let's merge when the CI is green 🥳