[1.13.2] Mapping non-empty LazyOptional to empty LazyOptional

[Choonster]

I have this method that gets a LazyOptional of a player's inventory IItemHandler and searches for the first slot with an item that matches a predicate. If it finds a valid item, it returns a LazyOptional of a single-slot IItemHandler that wraps that slot. If it doesn't, it returns an empty LazyOptional.

 

Currently there's no direct way for LazyOptional#map to transform a non-empty LazyOptional into an empty one, so I've had to use EmptyHandler.INSTANCE as a sentinel value and call LazyOptional#filter to transform that value into an empty LazyOptional.

 

My main concern is that LazyOptional#filter has a comment inside saying "Should we allow this function at all?" due to it being a non-lazy operation, so I'm somewhat reluctant to use it.

 

Java's Optional#map allows the function to return null to create an empty Optional, but Forge's LazyOptional#map uses a NonNullFunction so returning null isn't an option.

 

Is there a better way to map a non-empty LazyOptional into an empty one?

[lehjr]

What about returning Optional.empty() ?

[Choonster]

55 minutes ago, lehjr said:

What about returning Optional.empty() ?

 

Do you mean changing the lambda passed to LazyOptional#map to return Optional<IItemHandler> instead of just IItemHandler? I suppose that could work, though it seems a bit weird to nest the two different optional classes like that.