How to clone object in Kotlin?

Question

The Kotlin documentation describes cloning only in accessing Java and in enum class. In latter case clone is just throwing an exception.

So, how would I / should I clone arbitrary Kotlin object?

Should I just use clone() as in Java?

Answer 1

For a data class, you can use the compiler-generated copy() method. Note that it will perform a shallow copy.

To create a copy of a collection, use the toList() or toSet() methods, depending on the collection type you need. These methods always create a new copy of a collection; they also perform a shallow copy.

For other classes, there is no Kotlin-specific cloning solution. You can use .clone() if it suits your requirements, or build a different solution if it doesn't.

Answer 2

You can use Gson library to convert the original object to a String and then convert back that String to an actual Object type, and you'll have a clone. Although this is not the intended usage of the Gson library which is actually used to convert between JSON and other object types, but I have devised this method to solve the cloning problem in many of my Kotlin based Android applications. See my example. Put this function in the class/model of which you want to create a clone. In my example I'm cloning an Animal type object so I'll put it in the Animal class

class Animal{
 fun clone(): Animal 
 {
   val stringAnimal = Gson().toJson(this, Animal::class.java)
   return Gson().fromJson<Animal>(stringAnimal, Animal::class.java)
 }
}
       

Then use it like this:

val originalAnimal = Animal()
val clonedAnimal = originalAnimal.clone()

Answer 3

A Kotlin data class is easy to clone using .copy()

All values will be shallow copied, be sure to handle any list/array contents carefully.

A useful feature of .copy() is the ability to change any of the values at copy time. With this class:

data class MyData(
    val count: Int,
    val peanuts: Int?,
    val name: String
)
val data = MyData(1, null, "Monkey")

You could set values for any of the properties

val copy = data.copy(peanuts = 100, name = "Elephant")

The result in copy would have values (1, 100, "Elephant")