Ball and Chain: toSingleBox now sets up the failure chain properly.

[Shadowfiend]

The ParamFailure that toSingleBox returns when there are Failures in the list
now has a chain of Failures on it that correspond to all of the Failures in the
list.

[farmdawgnation]

Hmmm. So, I'm going to be honest. I'm not in love with this. Mostly because I always understood the semantic meaning of the chain parameter to have a causal relationship to the current failure. This is true in the case of the topmost ParamFailure, but not true of the first Failure whose chain is an earlier Failure in the List.

Do you see what I mean?

One possible iteration from this point is to have the topmost ParamFailure's chain be a ParamFailure[List[Failure]]. Thoughts?

[Shadowfiend]

I do see what you mean, but I don't think it's a problem. I'll think about it some more. Making the param the list of failures isn't terrible, but if another failure in turn is wrapped around the param, you lose the original list and that means you've lost information about what you were trying to do. Not the end of the world, but if we can represent both I think it's a win.

[Shadowfiend]

So yeah, I've thought about this some more. It's not the cleanest possible implementation, I agree, but using the param in a ParamFailure runs into type erasure issues (to properly extract it, you use a pattern match, and to properly pattern match the type, you'll have to pattern match on : List[Failure], and that causes erasure issues). So I think the API usability of the chain wins out over the ParamFailure for something that I think will be common if, say, people use this for form validation.

[farmdawgnation]

< headscratch >

Yeah, I see what you mean.

Do you think a subclass of ParamFailure that is returned from toSingleBox would be a net-win? For example, CompositeFailure such that:

case class CompositeFailure[T](message: String, failures: List[Failure], param: T) extends ParamFailure[T]

The question here is, I guess, "Do we gain any API niceness by adding to the class hierarchy?"

[farmdawgnation]

It occurs to me though that we're at the point where this conversation might should be happening on the ML...

[Shadowfiend]

Yeah, you're probably right.

[Shadowfiend]

Sent a summary to the list.

[farmdawgnation]

🎊

[Shadowfiend]

We didn't really reach a conclusion on this on the mailing list. Thoughts on what to do next? Shall I revive the thread?

[farmdawgnation]

Yeah, let's revive the thread. If nobody else objects I'm fine with including it. My objection is primarily over semantic meaning, and it's probably nitpicking for perfection in an imperfect situation. ;)

[Shadowfiend]

No further feedback was had, so I guess let's do it?

[farmdawgnation]

I'm down.