Equals method for data class in Kotlin

Question

I have the following data class

data class PuzzleBoard(val board: IntArray) {
    val dimension by lazy { Math.sqrt(board.size.toDouble()).toInt() }
}
         


        

Answer 1

In Kotlin, equals() behaves differently between List and Array, as you can see from code below:

val list1 = listOf(1, 2, 3)
val list2 = listOf(1, 2, 3)

val array1 = arrayOf(1, 2, 3)
val array2 = arrayOf(1, 2, 3)

//Side note: using a==b is the same as a.equals(b)

val areListsEqual = list1 == list2// true
val areArraysEqual = array1 == array2// false

List.equals() checks whether the two lists have the same size and contain the same elements in the same order.

Array.equals() simply does an instance reference check. Since we created two arrays, they point to different objects in memory, thus not considered equal.

Since Kotlin 1.1, to achieve the same behavior as with List, you can use Array.contentEquals().

Source: Array.contentEquals() docs ; List.equals() docs