Tracking Issue for PeekableIterator · Issue #132973 · rust-lang/rust (original) (raw)

Skip to content

Navigation Menu

• • GitHub Copilot Write better code with AI
  • GitHub Advanced Security Find and fix vulnerabilities
  • Actions Automate any workflow
  • Codespaces Instant dev environments
  • Issues Plan and track work
  • Code Review Manage code changes
  • Discussions Collaborate outside of code
  • Code Search Find more, search less
• Explore
  • Learning Pathways
  • Events & Webinars
  • Ebooks & Whitepapers
  • Customer Stories
  • Partners
  • Executive Insights
• • GitHub Sponsors Fund open source developers
  • The ReadME Project GitHub community articles
• • Enterprise platform AI-powered developer platform
• Pricing

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Sign up

Description

Feature gate: #![feature(peekable_iterator)]

This is a tracking issue for the PeekableIterator trait, which extends Iterator with peek and related methods that inspect the next element without consuming it.

Public API

// core::iter

pub trait PeekableIterator: Iterator { type PeekedItem<'a>: BorrowSelf::Item + 'a where Self: 'a; fn peek(&self) -> Option<PeekedItem<'_>>; fn next_if(&mut self, func: impl FnOnce(&Self::Item) -> bool) -> OptionSelf::Item; fn next_if_eq(&mut self, expected: &T) -> OptionSelf::Item where Self::Item: PartialEq, T: ?Sized; }

Steps / History

• ACP: Peek trait for peekable iterators libs-team#176
• Implementation: Add PeekableIterator trait #132976
• Final comment period (FCP)1
• Stabilization PR

Unresolved Questions

• Should peek take &mut self or &self? &self makes sense for iterators such as core::slice::iter but precludes implementing the trait on Peekable.
• What about the return type of peek? We could always make it return Self::Item like itertools’s PeekingNext, but that would prevent this trait from being implemented for consuming iterators such as vec::IntoIter, as well as Peekable itself.
  • If we use an associated type, then what should be the bound for it: Borrow, AsRef, or something else?

1. https://std-dev-guide.rust-lang.org/feature-lifecycle/stabilization.html ↩