Function successors

pub fn successors<T, F>(first: Option<T>, succ: F) -> Successors<T, F> 
where
    F: FnMut(&T) -> Option<T>,

Creates an iterator which, starting from an initial item, computes each successive item from the preceding one.

This iterator stores an optional item (Option<T>) and a successor closure (impl FnMut(&T) -> Option<T>). Its next method returns the stored optional item and if it is Some(val) calls the stored closure on &val to compute and store its successor. The iterator will apply the closure successively to the stored option’s value until the option is None. This also means that once the stored option is None it will remain None, as the closure will not be called again, so the created iterator is a FusedIterator. The iterator’s items will be the initial item and all of its successors as calculated by the successor closure.

use std::iter::successors;

let powers_of_10 = successors(Some(1_u16), |n| n.checked_mul(10));
assert_eq!(powers_of_10.collect::<Vec<_>>(), &[1, 10, 100, 1_000, 10_000]);