How to modify the parameter pass to kotlin data class?

Question

Say I have a data class

data class MyClass(val crop: Rect, val name: String)

But I want to make a copy of the Rect passed in since I don't want the value to be modified later. I don't want to the caller to call

MyClass(Rect(inCrop), "name")

in the code. How can I do this in my data class?

Thanks.

Answer 1

One workaround I can think of is:

data class MyClass(private var privateCrop: Rect, val name: String) {
    val crop get() = privateCrop

    init {
        privateCrop = Rect(privateCrop)
    }
}

You make crop private and make it a var (privateCrop), then you add a public getter for it. Now you can copy it in an init block.

But I gotta admit, this is rather ugly. The better solution here I think is to change Rect to be immutable, but if Rect isn't in your control, then I guess it can't be helped. You might also consider using a regular class.

Answer 2

You may not want to alter data class's like this. As per another solution's answer, you may find other peculiarities with this solution. The solution given by @Sweeper, also does not include providing a defensive copy, which you may want to do to avoid access to modifying the internal property field.