Function nom::lib::std::iter::unfold

Important traits for Unfold<St, F>

impl<St, T, F> Iterator for Unfold<St, F> where
    F: FnMut(&mut St) -> Option<T>,  type Item = T;

pub fn unfold<St, T, F>(initial_state: St, f: F) -> Unfold<St, F> where
    F: FnMut(&mut St) -> Option<T>, 

🔬 This is a nightly-only experimental API. (iter_unfold)

Creates a new iterator where each iteration calls the provided closure F: FnMut(&mut St) -> Option<T>.

This allows creating a custom iterator with any behavior without using the more verbose syntax of creating a dedicated type and implementing the Iterator trait for it.

In addition to its captures and environment, the closure is given a mutable reference to some state that is preserved across iterations. That state starts as the given initial_state value.

Note that the Unfold iterator doesn’t make assumptions about the behavior of the closure, and therefore conservatively does not implement FusedIterator, or override Iterator::size_hint from its default (0, None).

Examples

Let’s re-implement the counter iterator from module-level documentation:

#![feature(iter_unfold)]
let counter = std::iter::unfold(0, |count| {
    // Increment our count. This is why we started at zero.
    *count += 1;

    // Check to see if we've finished counting or not.
    if *count < 6 {
        Some(*count)
    } else {
        None
    }
});
assert_eq!(counter.collect::<Vec<_>>(), &[1, 2, 3, 4, 5]);