Function iterator_from 

pub fn iterator_from<T, F: FnMut() -> Option<T>>(
    f: F,
) -> impl Iterator<Item = T>

Turn a closure into an iterator.

Each next() on the iterator will simply call the closure once. The iterator ends when the closure returns None. The closure will not be called again after that point, even if next() is called again.

Example

use ad_hoc_iterator::iterator_from;

fn count_from_to(n: usize, m: usize) -> impl Iterator<Item = usize> {
    let mut i = n;
    iterator_from(move || {
        if i < m {
            i += 1;
            Some(i - 1)
        } else {
            None
        }
    })
}

Examples found in repository

examples/playground.rs (lines 17-24)

fn count_from_to(n: usize, m: usize) -> impl Iterator<Item = usize> {
    let mut i = n;
    iterator_from(move || {
        if i < m {
            i += 1;
            Some(i - 1)
        } else {
            None
        }
    })
}