Building Multiplatform apps

Using Swift
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I wondered if with Swift something like Kotlin Multiplatform is possible as well.

So that all the core logic would be written in Swift and for the UI I would use the native stack of the platform itself. Currently I'm not planning to build an app that requires a version for Apple, Android, Linux, Windows, and web. But I'm curious if someone has already some experience in creating a monorepo for all that platform that is scalable and maintainable. How much effort would this take to make that possible?

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This is basically the approach that The Browser Company has taken and applied successfully for Arc and Dia. Both are extremely large projects and it has worked quite well.

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Take a look at @keeshux's blog series about doing that with CMake, including his OSS app with all the source.

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This exists for Android (writing Swift, and running on Android)

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Hi Roman!

I've been doing this for a while in a decently complex app, and I would say that the approach depends on several factors stemming from your app domain. To name a few:

  1. What's your "core logic" made of? As in, is the app more UI or logic?
  2. How does your data flow? Is it UI → Core (pull) or do you also need events/callback behavior like Core → UI (push)?
  3. How asynchronous do you want it to be?
  4. Is the Core platform-agnostic or very tied to the platform differences?
  5. Do you have non-Swift dependencies?
  6. Do you use SwiftPM or CMake?

I believe the answer to these questions could make the choice of sharing Swift logic a great bet or a lot of extra work. By that, I mean that in some cases, duplicating the native code could lead, paradoxically, to less maintenance than designing a shared core that fits heterogeneous platforms and programming languages.

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Ah true, is their browser closed source, right?

I would like to see an real world project repo how they set it up. Do you know any?

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No, I don't think that there is anything that demonstrates that at the moment.

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Hey @compnerd , @Finagolfin , @mikaelacaron , @keeshux

Thank you very much for your replies.

I just recently saw this post which looks interesting: Bringing Goodnotes to the web with Swift and WebAssembly | Swift.org

But probably I had a wrong understanding about Swift + WASM. For me it would be nice if I could share "Core logic“ (network calls, data models, etc.) between all platforms and just have a different UI on every platform. But I think this isn't possible, right?

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Did you read @keeshux's blog series that I linked you? I believe he is doing exactly that.

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That is exactly the model that I was mentioning upthread. The model that The Browser Company uses is precisely this: the core Arc/Dia logic is shared, and the UI layer is per platform (Windows using the Windows UI primitives and macOS using the macOS UI primitives).

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@Finagolfin , @compnerd

Yes true, I was more thinking of the networking + Codable and JSONDecoder /Encoder, if this will work on all platforms. Probably when I would use the Async HTTP Client it would work, right?

Currently I will start with a SwiftUI client + Vapor backend and Core library for sharing types, maybe later I will expand to more platforms based on demand. Would you recommend going for a mono or multi repo when starting out with the project?

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Many core libraries work but there are API gaps on some platforms, and as for general Swift packages, you can check the index for platform compatibility. I have never built a full Swift GUI app, only command-line executables, so can't answer questions about repo organization and so on.

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