| <!DOCTYPE html><html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><meta name="generator" content="rustdoc"><meta name="description" content="Source of the Rust file `/root/.cargo/registry/src/github.com-1ecc6299db9ec823/itertools-0.10.5/src/peek_nth.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>peek_nth.rs - source</title><link rel="preload" as="font" type="font/woff2" crossorigin href="../../SourceSerif4-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../FiraSans-Regular.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../FiraSans-Medium.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../SourceCodePro-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../SourceSerif4-Bold.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../SourceCodePro-Semibold.ttf.woff2"><link rel="stylesheet" href="../../normalize.css"><link rel="stylesheet" href="../../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" href="../../ayu.css" disabled><link rel="stylesheet" href="../../dark.css" disabled><link rel="stylesheet" href="../../light.css" id="themeStyle"><script id="default-settings" ></script><script src="../../storage.js"></script><script defer src="../../source-script.js"></script><script defer src="../../source-files.js"></script><script defer src="../../main.js"></script><noscript><link rel="stylesheet" href="../../noscript.css"></noscript><link rel="alternate icon" type="image/png" href="../../favicon-16x16.png"><link rel="alternate icon" type="image/png" href="../../favicon-32x32.png"><link rel="icon" type="image/svg+xml" href="../../favicon.svg"></head><body class="rustdoc source"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="sidebar"><a class="sidebar-logo" href="../../itertools/index.html"><div class="logo-container"><img class="rust-logo" src="../../rust-logo.svg" alt="logo"></div></a></nav><main><div class="width-limiter"><nav class="sub"><a class="sub-logo-container" href="../../itertools/index.html"><img class="rust-logo" src="../../rust-logo.svg" alt="logo"></a><form class="search-form"><div class="search-container"><span></span><input class="search-input" name="search" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"><div id="help-button" title="help" tabindex="-1"><a href="../../help.html">?</a></div><div id="settings-menu" tabindex="-1"><a href="../../settings.html" title="settings"><img width="22" height="22" alt="Change settings" src="../../wheel.svg"></a></div></div></form></nav><section id="main-content" class="content"><div class="example-wrap"><pre class="src-line-numbers"><span id="1">1</span> |
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| </pre><pre class="rust"><code><span class="kw">use </span><span class="kw">crate</span>::size_hint; |
| <span class="kw">use </span><span class="kw">crate</span>::PeekingNext; |
| <span class="kw">use </span>alloc::collections::VecDeque; |
| <span class="kw">use </span>std::iter::Fuse; |
| |
| <span class="doccomment">/// See [`peek_nth()`] for more information. |
| </span><span class="attribute">#[derive(Clone, Debug)] |
| </span><span class="kw">pub struct </span>PeekNth<I> |
| <span class="kw">where |
| </span>I: Iterator, |
| { |
| iter: Fuse<I>, |
| buf: VecDeque<I::Item>, |
| } |
| |
| <span class="doccomment">/// A drop-in replacement for [`std::iter::Peekable`] which adds a `peek_nth` |
| /// method allowing the user to `peek` at a value several iterations forward |
| /// without advancing the base iterator. |
| /// |
| /// This differs from `multipeek` in that subsequent calls to `peek` or |
| /// `peek_nth` will always return the same value until `next` is called |
| /// (making `reset_peek` unnecessary). |
| </span><span class="kw">pub fn </span>peek_nth<I>(iterable: I) -> PeekNth<I::IntoIter> |
| <span class="kw">where |
| </span>I: IntoIterator, |
| { |
| PeekNth { |
| iter: iterable.into_iter().fuse(), |
| buf: VecDeque::new(), |
| } |
| } |
| |
| <span class="kw">impl</span><I> PeekNth<I> |
| <span class="kw">where |
| </span>I: Iterator, |
| { |
| <span class="doccomment">/// Works exactly like the `peek` method in `std::iter::Peekable` |
| </span><span class="kw">pub fn </span>peek(<span class="kw-2">&mut </span><span class="self">self</span>) -> <span class="prelude-ty">Option</span><<span class="kw-2">&</span>I::Item> { |
| <span class="self">self</span>.peek_nth(<span class="number">0</span>) |
| } |
| |
| <span class="doccomment">/// Returns a reference to the `nth` value without advancing the iterator. |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ```rust |
| /// use itertools::peek_nth; |
| /// |
| /// let xs = vec![1,2,3]; |
| /// let mut iter = peek_nth(xs.iter()); |
| /// |
| /// assert_eq!(iter.peek_nth(0), Some(&&1)); |
| /// assert_eq!(iter.next(), Some(&1)); |
| /// |
| /// // The iterator does not advance even if we call `peek_nth` multiple times |
| /// assert_eq!(iter.peek_nth(0), Some(&&2)); |
| /// assert_eq!(iter.peek_nth(1), Some(&&3)); |
| /// assert_eq!(iter.next(), Some(&2)); |
| /// |
| /// // Calling `peek_nth` past the end of the iterator will return `None` |
| /// assert_eq!(iter.peek_nth(1), None); |
| /// ``` |
| </span><span class="kw">pub fn </span>peek_nth(<span class="kw-2">&mut </span><span class="self">self</span>, n: usize) -> <span class="prelude-ty">Option</span><<span class="kw-2">&</span>I::Item> { |
| <span class="kw">let </span>unbuffered_items = (n + <span class="number">1</span>).saturating_sub(<span class="self">self</span>.buf.len()); |
| |
| <span class="self">self</span>.buf.extend(<span class="self">self</span>.iter.by_ref().take(unbuffered_items)); |
| |
| <span class="self">self</span>.buf.get(n) |
| } |
| } |
| |
| <span class="kw">impl</span><I> Iterator <span class="kw">for </span>PeekNth<I> |
| <span class="kw">where |
| </span>I: Iterator, |
| { |
| <span class="kw">type </span>Item = I::Item; |
| |
| <span class="kw">fn </span>next(<span class="kw-2">&mut </span><span class="self">self</span>) -> <span class="prelude-ty">Option</span><<span class="self">Self</span>::Item> { |
| <span class="self">self</span>.buf.pop_front().or_else(|| <span class="self">self</span>.iter.next()) |
| } |
| |
| <span class="kw">fn </span>size_hint(<span class="kw-2">&</span><span class="self">self</span>) -> (usize, <span class="prelude-ty">Option</span><usize>) { |
| size_hint::add_scalar(<span class="self">self</span>.iter.size_hint(), <span class="self">self</span>.buf.len()) |
| } |
| } |
| |
| <span class="kw">impl</span><I> ExactSizeIterator <span class="kw">for </span>PeekNth<I> <span class="kw">where </span>I: ExactSizeIterator {} |
| |
| <span class="kw">impl</span><I> PeekingNext <span class="kw">for </span>PeekNth<I> |
| <span class="kw">where |
| </span>I: Iterator, |
| { |
| <span class="kw">fn </span>peeking_next<F>(<span class="kw-2">&mut </span><span class="self">self</span>, accept: F) -> <span class="prelude-ty">Option</span><<span class="self">Self</span>::Item> |
| <span class="kw">where |
| </span>F: FnOnce(<span class="kw-2">&</span><span class="self">Self</span>::Item) -> bool, |
| { |
| <span class="self">self</span>.peek().filter(|item| accept(item))<span class="question-mark">?</span>; |
| <span class="self">self</span>.next() |
| } |
| } |
| </code></pre></div> |
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