kotlin fold

The fold function in Kotlin is used to iterate over a collection and accumulate a single value by applying a given operation on each element of the collection.

Here is an explanation of each step involved in using the fold function:

  1. The fold function takes two parameters: an initial value and an operation. The initial value is the starting value for the accumulation, and the operation is a lambda function that takes two arguments: the accumulated value so far and the current element of the collection.

  2. The fold function starts with the initial value and applies the operation to it and the first element of the collection.

  3. The result of the operation becomes the accumulated value for the next iteration, and the operation is applied to this accumulated value and the next element of the collection.

  4. This process continues until all elements of the collection have been processed.

  5. Finally, the fold function returns the final accumulated value.

Here is an example to illustrate the usage of fold:

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

val sum = numbers.fold(0) { acc, num ->
    acc + num
}

println(sum) // Output: 15

In this example, we have a list of numbers. We use the fold function to calculate the sum of these numbers. The initial value is 0, and the operation is addition (acc + num). The fold function starts with 0, adds the first number (1), then adds the second number (2), and so on until all numbers have been processed. The final accumulated value is the sum of all the numbers, which is 15.