foldIndexed<S> method Null safety

S foldIndexed<S>(
  1. S initial,
  2. IndexedAccumulate<S, E> f
)

Accumulates a collection to a single value of type S, which starts from an initial value, by combining each element with the current accumulator value, with the combinator f, providing sequential index of the element.

Example:

[1, 2, 5, 8].foldIndexed(0, (i, acc, x) => acc + (i % 2 * x)) // => 0 + 0 + 2 + 0 + 8 => 10

Implementation

S foldIndexed<S>(S initial, IndexedAccumulate<S, E> f) {
  var i = 0;
  return this?.fold<S>(initial, (p, e) => f(i++, p, e)) ?? initial;
}