Kotlin Fold

Kotlin Fold is a higher-order function in Kotlin that allows you to combine the elements of a collection into a single value. It is similar to the reduce function in Kotlin, but with one important difference – the initial value is passed as a parameter to fold, rather than being the first element of the collection.

Syntax

fun <T, R> Iterable<T>.fold(
    initial: R,
    operation: (acc: R, T) -> R
): R

The fold function takes an initial value of type R and a lambda function that combines the accumulator of type R and the next element of the collection of type T, and returns the result of the operation. The result of the fold operation is of type R.

Example

Suppose we have a list of integers, and we want to calculate the sum of all the even numbers in the list. We can achieve this using the fold function as follows:

val numbers = listOf(1, 2, 3, 4, 5, 6)

val sumOfEvens = numbers.fold(0) { acc, number ->
    if (number % 2 == 0) {
        acc + number
    } else {
        acc
    }
}

println(sumOfEvens) // Output: 12

In this code snippet, we initialize the accumulator to 0 and iterate through each number in the list. If the number is even, we add it to the accumulator. If the number is odd, we do not add it to the accumulator. The final result is the sum of all the even numbers in the list.

Conclusion

Kotlin Fold is a powerful function that can simplify many data processing operations. With its flexible syntax and easy-to-use lambda functions, it can help you manipulate data in complex ways with just a few lines of code.