What is the use of emptyArray() in Kotlin - kotlin

Question

I was learning emptyArray() in Kotlin, but I can't assign values in it (which is for obvious) and neither I can set it's size. What is the use of emptyArray in Kotlin?

Answer 1

There are cases where you want to fallback to an empty array or empty list. For example:
return someInputArray?.filterNotNull() ?: emptyArray()
In this case if I have a valid input array, I filter out null values, otherwise if the source array was null I return an empty array. Therefore an array is always returned instead of a null. Empty lists and arrays are probably more common than passing around nullable lists or arrays in Kotlin.
So yes, it is empty and you cannot add to it, just as no JVM array is expandable once allocated.

Answer 2

Similar to the java.util.Collections.emptyList() methods and its counterparts for Maps, etc., these methods are handy when you are calling a method which takes an array/collection as argument, but you don't want/need to provide any elements in that collection. You can either instantiate a new empty array/collection or use one of the helper methods.
If the above use case is very common in your scenario, you are safing memory by using the helpers as always the same instance is reused instead of creating new instances again and again. Otherwise it's mainly "syntax candy" making your code more readable and easier to understand.

Answer 3

emptyArray() function returns an empty array of size 0. it doesn't take any paramters (Nor size, neither elements). you can use it as rvalue in assignment operations. You can use empty array to dump all the values in a pre-existing arrays and set it's size to 0.
Note: it is better to return an empty than returning an array of nulls, as it'll not create any null point exceptions in further operations.
var array=arrayOf(1,2,3,4,5);
array = emptyArray() //The array datais dumped and size is set to 0;
array = arrayOf(0,1,2)

Answer 4

Arrays are fixed size containers. The emptyArray() function creates an array of 0 length, and you really can't do much with this. You can't store anything in it, and you can't resize it.
A common use case where you need an empty array would be as a default value for a property that will be set to a different array at a later point. This can be better than storing null in that property by default, because you don't have to deal with handling the possible null value when your code uses the array. For example, you can safely iterate over an empty array.
For a simple example:
class NumberHolder {
var numbers: Array<Int> = emptyArray()
fun printNumbers() {
numbers.forEach { println(it) }
}
}
The usage of this class would look something like this:
val nh = NumberHolder()
nh.printNumbers() // prints nothing
nh.numbers = arrayOf(1, 2, 3)
nh.printNumbers() // prints 1, 2, and 3 on separate lines