Function itertools::unfold [−][src]
pub fn unfold<A, St, F>(initial_state: St, f: F) -> Unfold<St, F>ⓘ where
F: FnMut(&mut St) -> Option<A>,
Creates a new unfold source with the specified closure as the “iterator function” and an initial state to eventually pass to the closure
unfold
is a general iterator builder: it has a mutable state value,
and a closure with access to the state that produces the next value.
This more or less equivalent to a regular struct with an Iterator
implementation, and is useful for one-off iterators.
// an iterator that yields sequential Fibonacci numbers, // and stops at the maximum representable value. use itertools::unfold; let mut fibonacci = unfold((1u32, 1u32), |(x1, x2)| { // Attempt to get the next Fibonacci number let next = x1.saturating_add(*x2); // Shift left: ret <- x1 <- x2 <- next let ret = *x1; *x1 = *x2; *x2 = next; // If addition has saturated at the maximum, we are finished if ret == *x1 && ret > 1 { None } else { Some(ret) } }); itertools::assert_equal(fibonacci.by_ref().take(8), vec![1, 1, 2, 3, 5, 8, 13, 21]); assert_eq!(fibonacci.last(), Some(2_971_215_073))