I have following case to model. There are devices,...

# announcements

[Czar]

I have following case to model. There are devices, all devices have some common set of properties, the rest of the properties wildly differ. I thought about using a sealed class hierarchy for them. E.g.

data class CommonProperties(/*properties here*/)
sealed class Device(val commonProperties: CommonProperties)
data class Type1Device(commonProperties: CommonProperties, /*other properties*/): Device(commonProperties)
//...

You probably see the problem: Data class primary constructor must have only property (val / var) parameters. Any suggestions on how to improve the design of my hierarchy?

[spand]

Considered putting the val commonProperties on an interface ?

[lupajz]

open val in sealed class header would not work ? or maybe just use class instead of data

[Czar]

@spand that does not change anything, same problem
@lupajz you mean override in every device type? Dirty. Not using data of course would work, but then I don't get all the niceties of data classes 🙂

[Czar]

@spand did you mean something like this:```data class CommonDeviceProperties()

sealed class Device {
abstract val commonDeviceProperties: CommonDeviceProperties
}

data class Type1Device(
override val commonDeviceProperties: CommonDeviceProperties, /*other properties*/
) : Device()```

[spand]

yes

[spand]

Although isnt that equivalent to adding an abstract property to Device ?

[lupajz]

open, yes

[Czar]

@spand, yes it is, and I already changed it locally like that 🙂 Thanks for the suggestion! I'll see how it works out in the end.

[Czar]

Updated the snippet.

[darkmoon_uk]

Members of a sealed class hierarchy don't have to be `data class`es, you could just have a regular class which would remove the need to compose the commonProperties in the way you've done, just use inheritance and put the properties in Device.