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kotlinlang

Is there a way to ensure a generic type is a data class?

I was trying to create a copy of a generic value which was only meant to be a data class

&gt; only meant to be a data class
Why? what's significant about a data class? Ultimately they're just normal classes with some functions generated for you, and even those functions can be overridden, so being a data class doesn't really get you anything.

I suppose. I guess I was trying to clone a generic type, and know that data classes have the `copy` method.

You could always make a `interface Copy&lt;T&gt; { fun copy(): T }`. Not sure how nicely it'll play with data classes though.

<@U0PR0TZ53> Data classes can't do that, as their generated `copy` functions all have different signatures (unfortunately Kotlin doesn't consider a function with all default parameters the same as a function with no parameters), so even though you can cal `copy()` on all of them, they get compiled down to different (unrelated) function calls.

Problem with the `interface Copy`, the `copy` function of a data class has an unknown signature, except for its name and return type

I see. That makes sense. Ended up using this interface:
```
interface Cloneable&lt;T&gt; {
    fun clone(): T
}
```
which in turn makes the data classes have this implementation:
```
data class User(val id: String) : Cloneable&lt;User&gt; {
    fun clone() = copy()
}
```

You can get a bit more type safety with `interface Cloneable&lt;T: Clonable&lt;T&gt;&gt;`