How to create a custom iterator in kotlin and add to existing class?-CodePudding

Hello I am trying to add a custom iterator for example to a Pair class from kotlin package to be able to use instance of that class in a for loop

Let's assume this is what I want to be able to do:

val pair: Pair<Int, String> = Pair(1, "sample data")
for (element in pair) {
println(element)
}

I know that there are plenty other ways to print elements from a pair but I specifically want to be able to use pair in a for loop and I need to add iterator() object with next() and hasNext() methods implementation to Pair class

CodePudding user response：

You can do this by providing the iterator() operator for your object, either as a member function or extension function. Example using an extension function:

fun main() {
    val pair: Pair<Int, String> = Pair(1, "sample data")
    for (element in pair) {
        println(element)
    }
}

operator fun <T> Pair<T, T>.iterator(): Iterator<T> = listOf(first, second).iterator()

However, you need to be aware that this way you partially lose strongly typing. element can only be a common supertype of all elements, in most cases simply Any?.

You can read more about this in the official documentation: https://kotlinlang.org/docs/control-flow.html#for-loops