Differences with bevy_reflect

[axelkar]

Bevy is a game engine written in Rust, and it has a reflection library: https://docs.rs/bevy_reflect/latest/bevy_reflect/

[fasterthanlime]

So I've been explicitly avoiding looking at their design thus far, to kind of keep a clean head.

One difference I know on top of my head is that bevy_reflect has a "type registry", whereas facet has an associated const.

Ideally, as const capabilities improve in Rust, it'll be possible to do all sorts of things in const fn contexts based on Facet's data structures. For now there are blockers (ConstTypeId shenanigans, PartialEq::eq in const, rescursive consts etc.) — but those are being discussed by various rust teams.

I think in terms of performance there are different goals, too — but again, I feel like if I took a detailed look at bevy_reflect it would kind of anchor my expectations and it would make it harder to just think from first principles so I'm going to willingly avoid doing that, and I'd be grateful if folks can exercise patience and not list too many differences in this topic right now yet.

[MrGVSV]

Hey @fasterthanlime, Bevy's SME-Reflect here! I know you haven't looked at bevy_reflect in detail (which is totally understandable and something I tend to do as well), but I was curious about facet-reflect's goals as that could help us answer similar questions from people on our end.

Since Bevy is a game engine, one thing we want to support as easily as possible is scripting and types fully defined at runtime (e.g. from a scripting language). We're not fully there yet, but that is one of our goals.

Is this a similar goal for facet-reflect? To allow for fully runtime-defined types that aren't strictly tied to things like TypeIds and such?

[fasterthanlime]

Hi there. Supporting non-static shapes was not necessarily on my radar, but someone's working on it, cf. #462

I'm not exactly sure what the goals of Facet are. For me, I would like to displace serde and syn and clap with it and crates based on it in my projects. I think a lot of people might be interested in making the same compromise.

I have not looked at anything Bevy related because, in my mind, it's unlikely that something made for a game engine will be suitable for my use case. It'll be likely that we have different goals. But there will be a point in the future where I think I've explored the space, and then I'm ready to look at Bevy Reflect and see if there are any commonalities that we can work on together — if that's what you had in mind in your comment — if not, then never mind, me.

I'm sorry that you're in a position where you have to tell people you don't really know what's going on either, but hopefully, the mere existence of facet is not threatening enough to cause you any real problems!

[MrGVSV]

Supporting non-static shapes was not necessarily on my radar, but someone's working on it, cf. #462

I'm not exactly sure what the goals of Facet are. For me, I would like to displace serde and syn and clap with it and crates based on it in my projects. I think a lot of people might be interested in making the same compromise.

Good to know! Yeah that's a great goal (and one I think much of the Rust community agrees is needed). That PR looks really nice as well. I've wanted to clean up bevy_reflect in a similar way.

I have not looked at anything Bevy related because, in my mind, it's unlikely that something made for a game engine will be suitable for my use case. It'll be likely that we have different goals. But there will be a point in the future where I think I've explored the space, and then I'm ready to look at Bevy Reflect and see if there are any commonalities that we can work on together — if that's what you had in mind in your comment — if not, then never mind, me.

No that totally makes sense. While bevy_reflect is meant to be generally useful outside of Bevy, it's primary goal is to serve the game engine, so we have to make compromises for that in ways that a true Rust reflection crate might not.

But yeah if you ever do take a look at bevy_reflect (please don't feel like you need to at all), it would be really cool to get your insight and swap notes—hopefully for the benefit of both projects.

I'm sorry that you're in a position where you have to tell people you don't really know what's going on either, but hopefully, the mere existence of facet is not threatening enough to cause you any real problems!

Don't be sorry! This is just what happens when people get really excited about a project haha. And for good reason too. I'm excited to see how facet progresses :)