Question about the interop layer

[carozo]

Hi,
I'm trying to better understand the new architecture and the interop layer, and I have some questions that I haven't been able to find answers to in documentation. However, if there's documentation on the topic that answers my questions, feel free to point me to it.

From what I've read here, I understand that the interop layer is Fabric-centered. For instance:

The interop layer (...) is a platform layer that allows you to register legacy components into the New Renderer (aka Fabric) and it maps legacy function invocation (for example, the setters for specific properties) to the equivalent in the New Renderer.

This makes me wonder about TurboModules:

• Does an interop layer exist for older bridge modules as well, modules that do not require rendering? I've also noticed some error messages logging "TurboModules interop: false", which adds to my confusion. If this layer exists, is it documented somewhere? I'd like to know how it works.
• If a module has not been migrated to the new architecture, how does it sometimes still work even in bridgeless mode?
• Provided that there exists an interop layer that makes old modules work in bridgeless mode, would it be OK to never update a library if there's no need to make use of React 18 concurrent features? Or is that layer eventually going to be removed, has some performance compromises, or anything that would make it only a transitional state?

Sorry in advance if my questions are basic, naive or based on wrong premises. Any help would be greatly appreciated. Thanks!

[cortinico]

Interop Layer is an umbrella term that we used to refer to every backward compatible API we introduced to make it easer to adopt the New Architecture.
What you linked to is the Fabric Interop Layer, but there are also other APIs that are part of the Interop Layer.

• Does an interop layer exist for older bridge modules as well, modules that do not require rendering? I've also noticed some error messages logging "TurboModules interop: false", which adds to my confusion. If this layer exists, is it documented somewhere? I'd like to know how it works.

Yes there is indeed a Modules Interop Layer. We don't have public documentation about it that I recall. Practically speaking, you'll be able to still load your legacy modules even in bridgeless mode through the TurboModuleRegistry.

• If a module has not been migrated to the new architecture, how does it sometimes still work even in bridgeless mode?

Because of the Interop Layer I mentioned above. Particularly there is no need for you to do anything or turn on/off any configuration. It should just work.

• Provided that there exists an interop layer that makes old modules work in bridgeless mode, would it be OK to never update a library if there's no need to make use of React 18 concurrent features? Or is that layer eventually going to be removed, has some performance compromises, or anything that would make it only a transitional state?

We're planning to sunset those Interop Layers sometime in the future. As you can imagine those are technical debt and are impacting the overall app size (because we're shipping both old and new arch) so you should be looking into migrating away from the legacy APIs as soon as it's convenient to you.

[carozo]

Very clear answer, thank you for taking the time