How to clone object in Kotlin?

Question

The question is that simple.

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

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

Here is a consistent solution that works for any object type:

Kotlin's Array data structure provides a clone() method that can be used to clone the contents of the array:

val a = arrayOf(1)
//Prints one object reference
println(a)     
//Prints a different object reference
println(a.clone())

As of Kotlin 1.3, the clone method has been supported on all major targets, so it should be usable across platforms.

Answer 3

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

All values with 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")