Hello everyone. I've been playing with multiplatform a bit and I'm wondering if anyone has some insight on the pros/cons of using

expect/actual

vs using an interface. I'm especially curious if there are use cases for

expect/actual

that can't be solved with an interface or are obviously better suited to the

expect/actual

pattern. I asked a question on the forums, but it didn't get any traction.

From my experience, you should only use expect/actual for concrete implementations and thus they be should be rare. Interfaces are definitely what I lean on the most.

If you need to instantiate the class from common code then expect/actual will help make that cleaner. To create platform instances from common code without expect/actual would be ugly. You would need some sort of factory class passed into your common code everywhere. The two can definitely be used together. In one project I had a repository interface declared, mostly as a testing seam. Then I had an Android and iOS implementation that wrote data to the file systems of each platform. The class calling that code took the repo as a constructor parameter with a default value set as the file based repo class.

As a more concrete example: input. The current (early/prototyping) state of my app uses numbered menus printed to the console and takes numeric input from the user to make a selection. The options I see for obtaining the input (platform-dependent): 1. Create a top-level

expect fun getNumericInput(): Int

or

expect class MenuIO

where I keep all the necessary IO functions 2. Create an

interface MenuIO

that I implement and inject from the platform-level entry points. It seems to me that the general rule you're both getting at could be stated "interfaces for injectables and expect/actual for newables" (assuming the injectable/newable dichotomy)