Hi here! How do you usually handle code that is s...

# multiplatform

[Anton Afanasev]

Hi here!

How do you usually handle code that is sharable between platforms, but have unique or platform specific dependencies?
For instance my expected constructor has 1 mandatory argument that I would like to share between platforms.

expect class MailBox(firstName: String) {}

Now, I want that my Android actual implementation will have some Android specific object passed as well. Lets say Context
I can not do

actual class MailBox actual constructor(firstName: String, context: Context) // not allowed as actual constructor does not match the expected.

If I use a secondary constructor, I cannot be sure that it will be called and therefore Context is going to be of Nullable type and smell.

actual class MailBox actual constructor(firstName: String) {
    private var context: Context? = null // Context is of Nullable - not nice
    
    constructor(context: Context, firstName: String = "Bobby", ) : this(firstName) {
        this.context = context
    }

Obviously, I can declare my expected without primary constructor - but then I have no control over each platform passing a mandatory argument.

expect class MailBox {} //commonMain

actual class MailBox(context: Context, firstName: String) {} //androidMain

actual class MailBox(firstName: String) {} //iOSMain

//No ability to force passing `firstName` argument. Any platform can decide to modify/remove `firstName` on their will.

QUESTION: Are there any other, cleaner approaches that allows me to force some expected constructor values mandatory, while others can be platform specific?

[Dominaezzz]

Hmm, maybe use poly-morphism instead of expect / actual .

[kevindmoore]

Or just inject the context into that class

[russhwolf]

If firstName is mandatory then maybe you want

expect class Mailbox {
  val firstName
}

Then the `actual`s are forced to define it somehow, and the most natural path will be a constructor argument

actual class MailBox(firstName: String) {
  actual val firstName = firstName
}

But I agree that using an interface or abstract class might be nicer for this.

[Anton Afanasev]

Thanks for your input.
@russhwolf, I was not clear enough when defined firstName as "mandatory". By "mandatory" I meant that I would like to keep this value injected in the constructor no matter what platform it is. Like with expect/actual I force all the platforms to respect this protocol.
Thank you for your input