Kotlin data class copy method not deep copying all members
Solution 1:
The copy
method of Kotlin is not supposed to be a deep copy at all. As explained in the reference doc (https://kotlinlang.org/docs/reference/data-classes.html), for a class such as:
data class User(val name: String = "", val age: Int = 0)
the copy
implementation would be:
fun copy(name: String = this.name, age: Int = this.age) = User(name, age)
So as you can see, it's a shallow copy. The implementations of copy
in your specific cases would be:
fun copy(a: Int = this.a, bar: Bar = this.bar, list: MutableList<Int> = this.list) = Foo(a, bar, list)
fun copy(x: Int = this.x) = Bar(x)
Solution 2:
As @Ekeko said, the default copy()
function implemented for data class is a shallow copy which looks like this:
fun copy(a: Int = this.a, bar: Bar = this.bar, list: MutableList<Int> = this.list)
To perform a deep copy, you have to override the copy()
function.
fun copy(a: Int = this.a, bar: Bar = this.bar.copy(), list: MutableList<Int> = this.list.toList()) = Foo(a, bar, list)