inline fun <R> CharSequence.foldIndexed(
    initial: R,
    operation: (index: Int, acc: R, Char) -> R
): R

Accumulates value starting with initial value and applying operation from left to right to current accumulator value and each character with its index in the original char sequence.


operation - function that takes the index of a character, current accumulator value and the character itself, and calculates the next accumulator value.