A Better Peekable

This crate provides a trait BetterPeekable and a type BPeekable<I: Iterator> which is a wrapper over an iterator and returned by calling better_peekable() on any Iterator. You can call the usual iterator methods on BPeekable<I> just like next() on I. You can also call methods like next_back,size_hint and rposition and everything else from DoubleEndedIterator in addition to peek and peek_n.

peek gives you a reference to the immediately available item to be consumed by a next() call, whereas peek_n allows you to peek n times ahead. Calling peek_n(0) is the same as calling peek.

peek and peek_n are idempotent which means calling them repeatedly on BPeekable should have no effects on the underlying iterator or any state of BPeekable. If you find a bug that violates this contract, please open an issue.

Usage

Add to better_peekable to your Cargo.toml.

[dependencies]

better_peekable = "0.2.4"

We are going to test the idempotence of BPeekable using the following sequence of peek and peek_n calls.

// Required for peek and peek_n 
use better_peekable::BetterPeekable;

fn main() {
    let vec = vec![
            String::from("Hello"),
            String::from("World"),
            String::from("It's a nice day to make"),
            String::from("A better peekable iterator adaptor"),
            String::from("Peek_N and Peek are supposed to be"),
            String::from("Idempotent Methods"),
        ];

        let mut iter = vec.into_iter();
        let mut better_peeker = iter.better_peekable();
       
        assert_eq!(better_peeker.peek(), Some(&"Hello".to_string()));
        assert_eq!(better_peeker.peek(), Some(&"Hello".to_string()));
        assert_eq!(better_peeker.peek(), Some(&"Hello".to_string()));
        assert_eq!(better_peeker.peek_n(1), Some(&"World".to_string()));
        assert_eq!(better_peeker.next(), Some("Hello".to_string()));
        assert_eq!(better_peeker.next(), Some("World".to_string()));
        assert_eq!(
            better_peeker.peek(),
            Some(&"It's a nice day to make".to_string())
        );
        assert_eq!(
            better_peeker.peek_n(0),
            Some(&"It's a nice day to make".to_string())
        );
        assert_eq!(
            better_peeker.peek_n(1),
            Some(&"A better peekable iterator adaptor".to_string())
        );
        assert_eq!(
            better_peeker.nth(1),
            Some("A better peekable iterator adaptor".to_string())
        );
        assert_eq!(
            better_peeker.peek_n(1),
            Some(&"Idempotent Methods".to_string())
        );

Changelog 0.2.4 :

Removed trait bound std::fmt::Debug bound from Iterator::Item