You don't have many choices for cross-platform tools. You can either use C++ that is quite hard for a lot of people but I would say most popular and most stable. You can use C# or Java with Xamarin but it is very expensive, unstable and it is kind vendor lock-in. You can also use JavaScript but you will lose a lot of performance that is very important on mobile. There are other options like using Lua, RubyMotion but they suffer same problems as JavaScript
Bottom line: There isn't convenient, modern, fast, open-source method for cross-platform development.
Swift bridges nicely with C and it is built on LLVM so you will be able to use it on Android with Android NDK and bridge it through JNI and Microsoft recently also adopted LLVM so you will be also able to use it there.
Bottom line: There isn't convenient, modern, fast, open-source method for cross-platform development.
Swift bridges nicely with C and it is built on LLVM so you will be able to use it on Android with Android NDK and bridge it through JNI and Microsoft recently also adopted LLVM so you will be also able to use it there.