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[1.13.2] Mapping non-empty LazyOptional to empty LazyOptional


Choonster

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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?

Please don't PM me to ask for help. Asking your question in a public thread preserves it for people who are having the same problem in the future.

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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.

Please don't PM me to ask for help. Asking your question in a public thread preserves it for people who are having the same problem in the future.

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