MemoIter

A small Rust library implementing a Memoized Iterator, which pairs a normal Iterator<Item=T> with an owned Vec<T> to store the items it returns. Alternatively, it may be considered as a wrapped Vec<T> that is lazily populated with items from the Iterator.

This is useful for infinite Iterators where each value depends on the last, such as the factorial function: Calculating the factorial of 1000 is quite expensive, but it also includes, as byproducts, the factorials of 999, 998, and so on. If these are stored, they can be retrieved later, without needing to be recalculated for their own sake.

Example

The following example shows a MemoIter being used to cache the results of calculating the Fibonacci Sequence.

use memoiter::MemoIter;
use std::iter::successors;


fn main() {
    let mut fibonacci: MemoIter<_, u32> = successors(
        Some((0, 1)),
        |&(a, b)| Some((b, b + a)),
    ).map(|p| p.0).into();

    assert_eq!(fibonacci.get(0), Some(&0));
    assert_eq!(fibonacci.get(1), Some(&1));
    assert_eq!(fibonacci.get(4), Some(&3));
    assert_eq!(fibonacci.get(9), Some(&34));

    //  This value was calculated as a byproduct of calculating 4, and is simply
    //      retrieved here.
    assert_eq!(fibonacci.get(3), Some(&2));

    let (seq, _) = fibonacci.consume();
    assert_eq!(seq, [0, 1, 1, 2, 3, 5, 8, 13, 21, 34]);
}