what are the benefits of Xamarin using F# [if it is supported]
any comparison between Xamarin vs Kotlin?
F# is supported, though sometimes there are some quirks with it as it's not as high a priority as C#. Xamarin Live Player was written in F# for example.
The benefits are the same as the benefits of F# over C# - much less code, immutability by default, functional coding etc.
Kotlin runs on the JVM and can be used with Android, but not iOS. Xamarin is iOS, Android and macOS and you can code share with Windows apps. Xamarin forms is 99% code sharing for iOS, Android, macOS, WPF, UWP, Linux...
If you take the benefits of F# over C# and multiply that by about a thousand, you get the the benefits of Kotlin over Java.
but this app ecosystem is built like silos
why can all the companies microsoft, apple and google work on a shared model which benefits them and the developers?
There's no upside to Apple helping Android and vice versa - it's all about tying developers and apps to your ecosystem to drive sales, not about a percent cross-platform ecosystem that could drive sales away. After all if Apple cared about developers they would never have invented provisioning profiles!
This is where Microsoft can win - they have no loyalty to either platform and the Windows mobile platform is pretty much dead, so they can sell cross-platform tools that not only allow you to write iOS and Android apps, but can also be used for the entire Windows ecosystem, from desktop to hololens.
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