Make Facet take a specific command and be composable about amethyst HOT 9 OPEN

Okay. Let’s think about an example.

StairAscender
StairDescender

Compose into StairTraverser. That’s an additive composition.

For And and Or compositions I can’t think of an example off the top of my head. Both I think would require the two composited facets to take the same command though. An And/Or that takes different facets doesn’t make sense to me.

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would the API be facet.compose(otherFacet)

Or would it be better to have a CompositeFacet class that is a facet and has a constructor that takes two facets?

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I'd do this similar to how Behaviors are composed now. The reason for this is that we can take advantage of operator overloading and we can also define boolean operations like facet0 + facet1 facet0 or facet1, things like that.

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Okay. So basically. If I’m going to implement this look at how behavior composition works.

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That's a good idea, yes. But first let's think about the kinds of compositions we might want to implement. + can be used to compose but what about and and or? Do you think that would make sense here?

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So StairAscender takes GoUp and StairDescender takes GoDown so StairTraverser takes both GoUp and GoDown so it is an additive composition. Job well done, we can go home, right? 😄

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Yeah. I mean sure. My question was, is there a case where we’d want and/or style composition . What would that be useful for if anything?

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or/and I think is not really meaningful here. We have it with Behaviors and it is useful because they return a Boolean value so we can determine whether it performed an action or not. or short-circuits so if the first Behavior returns true the second is not run at all.

With Facets this is a bit more fuzzy because each Facet responds to a single Command so the composite Facet we get with + is just doing dynamic dispatch. As a corollary the or/and overloads seem useless here because if we have a Command we already know which Facet responds to that so there is no point in short-circuiting.

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