Ribbon - tape for Iterators

Ribbon is meant to provide API for holding (and thus making available) some number of items returned by iterators.

This is meant for cases where using iterators is convenient, but some context around the item returned by an iterator is needed. This is especially useful when look-ahead is necessary (we need to know what values come after the current one before deciding what to do with it).

This crate provides two types that implement the Ribbon trait:

• Tape: a dynamically sized Ribbon that can hold varying number of items and can grow and shrink as necessary. It is backed up by a VecDeque, and allocates memory on the heap (as is customary by dynamically sized collections)
• Band: a fix-sized Ribbon backed up by an array of N elements. It cannot grow over the given fixed length, and instead drops the first element if no space is available at the given moment.

Examples:

Using Tape

use ribbon::Tape;

let mut tape = Tape::new(0..10);
tape.expand_n(5);

assert_eq!(tape.len(), 5);
assert_eq!(tape.peek_front(), Some(&0));
assert_eq!(tape.peek_back(), Some(&4));

Using Band

use ribbon::Band;
use ribbon::Ribbon;

// Band with capacity for 5 items
let mut band: Band<3, _, _> = Band::new(0..4);
band.expand_n(2); // consume 0, 1 from iterator

assert_eq!(band.len(), 2);
assert_eq!(band.peek_front(), Some(&0));
assert_eq!(band.peek_back(), Some(&1));

// "slides" over the items from iterator -> returns first and expands by 1
assert_eq!(band.progress(), Some(0)); // consume 3 from iterator
assert_eq!(band.progress(), Some(1)); // consumes 4 from iterator, iterator has no more values

// iterator does not produce more values, progress becomes no-op.
assert_eq!(band.progress(), None);