Elmish pattern support

[xperiandri]

It would be nice to be able to develop Elm architecture apps with Avalonia like Elmish.XamarinForms

[jmacato]

It's a great architecture to play with (upon my cursory look at least) but this is something that the community will provide for themselves. I also dont see any technical challenges for Avalonia with regards to Elm/Model-View-Update architecture so i guess someone can take a shot at this? :)

[ma3yta]

example of DSL https://github.com/Dolfik1/AvaloniaDSL/blob/master/DSL/Main.fs
https://github.com/Lleutch/ElmishWPFLearning
https://github.com/elmish/Elmish.WPF/tree/master/src/Elmish.WPF

@cmeeren @Lleutch Could you please help Avalonia to implement Elmish?

[cmeeren]

That will likely be a bigger undertaking than I can commit to at the moment.

For a static view solution, it would probably be fairly easy - perhaps even trivial - to port Elmish.WPF, since Avalonia is similar to WPF. Anyone is welcome to have a go. If it turns out that the Binding and ViewModel code could be reused 100% (and if it's likely that it would continue to be the case in further development), I could consider extracting that to its own library. In any case, just as a start and proof of concept, a fork of Elmish.WPF could be made and adjusted to Avalonia. Refactoring can come later.

However, I don't really like Elmish with static views because of its significant limitations compared to dynamic views. Dynamic views, on the other hand, require a lot more work to implement. There are important performance considerations in order to ensure the view creation and reconciliation/updating is as efficient as possible (Fabulous still struggles with a few things in this regard), there must be a way to support 3rd party controls, and a code generator might be needed to make the dynamic view code maintanable (similar to Fabulous).

[Lleutch]

I completely agree with @cmeeren on each point raised.
Static views have their own limitations compared to dynamic ones. So I would go for implementing a dynamic DSL instead.
In addition a simple PoC might be a good starting point to show others the benefit of it (no need to worry about diff algorithm on tree for the moment, and things like that...)
And same as @cmeeren, I won't be able to undertake such a task for the moment.
However, you can contact me anytime, and I might be able to help out.

[cmeeren]

Regarding a DSL for dynamic views - there are several directions to take:

• List-based like Fable.React and Fabulous.SimpleElements
• Constructor-/overload-/optional arg-based like Fabulous
• CE-based like AvaloniaDSL

Aside from the syntax difference, when you delve deep enough into it, I'm sure all come with their own pros and cons regarding technical limitations.

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In addition a simple PoC might be a good starting point to show others the benefit of it (no need to worry about diff algorithm on tree for the moment, and things like that...)

I agree, a PoC might be a good starting point. I just want to note that sooner or later, performance will become a concern if it is ever supposed to be a viable way of creating real-life complex apps. It might therefore be prudent to have performance at the back of the mind even in the PoC stage, to ensure one doesn't end up with an implementation that is fundamentally inefficient and difficult to optimize.

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And same as @cmeeren, I won't be able to undertake such a task for the moment.
However, you can contact me anytime, and I might be able to help out.

I second that. While I can't commit to being a primus motor or maintainer, feel free to cc me for input.

[ma3yta]

https://github.com/JaggerJo/Avalonia.FuncUI

[xperiandri]

@ma3yta looks amazing!

[kekekeks]

This doesn't belong to the core avalonia repo, feel free to implement your own wrapper