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 <!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/adaptors/mod.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>mod.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="doccomment">//! Licensed under the Apache License, Version 2.0
 //! &lt;https://www.apache.org/licenses/LICENSE-2.0&gt; or the MIT license
 //! &lt;https://opensource.org/licenses/MIT&gt;, at your
 //! option. This file may not be copied, modified, or distributed
 //! except according to those terms.

 </span><span class="kw">mod </span>coalesce;
 <span class="kw">mod </span>map;
 <span class="kw">mod </span>multi_product;
 <span class="kw">pub use </span><span class="self">self</span>::coalesce::<span class="kw-2">*</span>;
 <span class="kw">pub use </span><span class="self">self</span>::map::{map_into, map_ok, MapInto, MapOk};
 <span class="attribute">#[allow(deprecated)]
 </span><span class="kw">pub use </span><span class="self">self</span>::map::MapResults;
 <span class="attribute">#[cfg(feature = <span class="string">&quot;use_alloc&quot;</span>)]
 </span><span class="kw">pub use </span><span class="self">self</span>::multi_product::<span class="kw-2">*</span>;

 <span class="kw">use </span>std::fmt;
 <span class="kw">use </span>std::iter::{Fuse, Peekable, FromIterator, FusedIterator};
 <span class="kw">use </span>std::marker::PhantomData;
 <span class="kw">use </span><span class="kw">crate</span>::size_hint;

 <span class="doccomment">/// An iterator adaptor that alternates elements from two iterators until both
 /// run out.
 ///
 /// This iterator is *fused*.
 ///
 /// See [`.interleave()`](crate::Itertools::interleave) for more information.
 </span><span class="attribute">#[derive(Clone, Debug)]
 #[must_use = <span class="string">&quot;iterator adaptors are lazy and do nothing unless consumed&quot;</span>]
 </span><span class="kw">pub struct </span>Interleave&lt;I, J&gt; {
     a: Fuse&lt;I&gt;,
     b: Fuse&lt;J&gt;,
     flag: bool,
 }

 <span class="doccomment">/// Create an iterator that interleaves elements in `i` and `j`.
 ///
 /// [`IntoIterator`] enabled version of `[Itertools::interleave]`.
 </span><span class="kw">pub fn </span>interleave&lt;I, J&gt;(i: I, j: J) -&gt; Interleave&lt;&lt;I <span class="kw">as </span>IntoIterator&gt;::IntoIter, &lt;J <span class="kw">as </span>IntoIterator&gt;::IntoIter&gt;
     <span class="kw">where </span>I: IntoIterator,
           J: IntoIterator&lt;Item = I::Item&gt;
 {
     Interleave {
         a: i.into_iter().fuse(),
         b: j.into_iter().fuse(),
         flag: <span class="bool-val">false</span>,
     }
 }

 <span class="kw">impl</span>&lt;I, J&gt; Iterator <span class="kw">for </span>Interleave&lt;I, J&gt;
     <span class="kw">where </span>I: Iterator,
           J: Iterator&lt;Item = I::Item&gt;
 {
     <span class="kw">type </span>Item = I::Item;
     <span class="attribute">#[inline]
     </span><span class="kw">fn </span>next(<span class="kw-2">&amp;mut </span><span class="self">self</span>) -&gt; <span class="prelude-ty">Option</span>&lt;<span class="self">Self</span>::Item&gt; {
         <span class="self">self</span>.flag = !<span class="self">self</span>.flag;
         <span class="kw">if </span><span class="self">self</span>.flag {
             <span class="kw">match </span><span class="self">self</span>.a.next() {
                 <span class="prelude-val">None </span>=&gt; <span class="self">self</span>.b.next(),
                 r =&gt; r,
             }
         } <span class="kw">else </span>{
             <span class="kw">match </span><span class="self">self</span>.b.next() {
                 <span class="prelude-val">None </span>=&gt; <span class="self">self</span>.a.next(),
                 r =&gt; r,
             }
         }
     }

     <span class="kw">fn </span>size_hint(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; (usize, <span class="prelude-ty">Option</span>&lt;usize&gt;) {
         size_hint::add(<span class="self">self</span>.a.size_hint(), <span class="self">self</span>.b.size_hint())
     }
 }

 <span class="kw">impl</span>&lt;I, J&gt; FusedIterator <span class="kw">for </span>Interleave&lt;I, J&gt;
     <span class="kw">where </span>I: Iterator,
           J: Iterator&lt;Item = I::Item&gt;
 {}

 <span class="doccomment">/// An iterator adaptor that alternates elements from the two iterators until
 /// one of them runs out.
 ///
 /// This iterator is *fused*.
 ///
 /// See [`.interleave_shortest()`](crate::Itertools::interleave_shortest)
 /// for more information.
 </span><span class="attribute">#[derive(Clone, Debug)]
 #[must_use = <span class="string">&quot;iterator adaptors are lazy and do nothing unless consumed&quot;</span>]
 </span><span class="kw">pub struct </span>InterleaveShortest&lt;I, J&gt;
     <span class="kw">where </span>I: Iterator,
           J: Iterator&lt;Item = I::Item&gt;
 {
     it0: I,
     it1: J,
     phase: bool, <span class="comment">// false ==&gt; it0, true ==&gt; it1
 </span>}

 <span class="doccomment">/// Create a new `InterleaveShortest` iterator.
 </span><span class="kw">pub fn </span>interleave_shortest&lt;I, J&gt;(a: I, b: J) -&gt; InterleaveShortest&lt;I, J&gt;
     <span class="kw">where </span>I: Iterator,
           J: Iterator&lt;Item = I::Item&gt;
 {
     InterleaveShortest {
         it0: a,
         it1: b,
         phase: <span class="bool-val">false</span>,
     }
 }

 <span class="kw">impl</span>&lt;I, J&gt; Iterator <span class="kw">for </span>InterleaveShortest&lt;I, J&gt;
     <span class="kw">where </span>I: Iterator,
           J: Iterator&lt;Item = I::Item&gt;
 {
     <span class="kw">type </span>Item = I::Item;

     <span class="attribute">#[inline]
     </span><span class="kw">fn </span>next(<span class="kw-2">&amp;mut </span><span class="self">self</span>) -&gt; <span class="prelude-ty">Option</span>&lt;<span class="self">Self</span>::Item&gt; {
         <span class="kw">let </span>e = <span class="kw">if </span><span class="self">self</span>.phase { <span class="self">self</span>.it1.next() } <span class="kw">else </span>{ <span class="self">self</span>.it0.next() };
         <span class="kw">if </span>e.is_some() {
             <span class="self">self</span>.phase = !<span class="self">self</span>.phase;
         }
         e
     }

     <span class="attribute">#[inline]
     </span><span class="kw">fn </span>size_hint(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; (usize, <span class="prelude-ty">Option</span>&lt;usize&gt;) {
         <span class="kw">let </span>(curr_hint, next_hint) = {
             <span class="kw">let </span>it0_hint = <span class="self">self</span>.it0.size_hint();
             <span class="kw">let </span>it1_hint = <span class="self">self</span>.it1.size_hint();
             <span class="kw">if </span><span class="self">self</span>.phase {
                 (it1_hint, it0_hint)
             } <span class="kw">else </span>{
                 (it0_hint, it1_hint)
             }
         };
         <span class="kw">let </span>(curr_lower, curr_upper) = curr_hint;
         <span class="kw">let </span>(next_lower, next_upper) = next_hint;
         <span class="kw">let </span>(combined_lower, combined_upper) =
             size_hint::mul_scalar(size_hint::min(curr_hint, next_hint), <span class="number">2</span>);
         <span class="kw">let </span>lower =
             <span class="kw">if </span>curr_lower &gt; next_lower {
                 combined_lower + <span class="number">1
             </span>} <span class="kw">else </span>{
                 combined_lower
             };
         <span class="kw">let </span>upper = {
             <span class="kw">let </span>extra_elem = <span class="kw">match </span>(curr_upper, next_upper) {
                 (<span class="kw">_</span>, <span class="prelude-val">None</span>) =&gt; <span class="bool-val">false</span>,
                 (<span class="prelude-val">None</span>, <span class="prelude-val">Some</span>(<span class="kw">_</span>)) =&gt; <span class="bool-val">true</span>,
                 (<span class="prelude-val">Some</span>(curr_max), <span class="prelude-val">Some</span>(next_max)) =&gt; curr_max &gt; next_max,
             };
             <span class="kw">if </span>extra_elem {
                 combined_upper.and_then(|x| x.checked_add(<span class="number">1</span>))
             } <span class="kw">else </span>{
                 combined_upper
             }
         };
         (lower, upper)
     }
 }

 <span class="kw">impl</span>&lt;I, J&gt; FusedIterator <span class="kw">for </span>InterleaveShortest&lt;I, J&gt;
     <span class="kw">where </span>I: FusedIterator,
           J: FusedIterator&lt;Item = I::Item&gt;
 {}

 <span class="attribute">#[derive(Clone, Debug)]
 </span><span class="doccomment">/// An iterator adaptor that allows putting back a single
 /// item to the front of the iterator.
 ///
 /// Iterator element type is `I::Item`.
 </span><span class="kw">pub struct </span>PutBack&lt;I&gt;
     <span class="kw">where </span>I: Iterator
 {
     top: <span class="prelude-ty">Option</span>&lt;I::Item&gt;,
     iter: I,
 }

 <span class="doccomment">/// Create an iterator where you can put back a single item
 </span><span class="kw">pub fn </span>put_back&lt;I&gt;(iterable: I) -&gt; PutBack&lt;I::IntoIter&gt;
     <span class="kw">where </span>I: IntoIterator
 {
     PutBack {
         top: <span class="prelude-val">None</span>,
         iter: iterable.into_iter(),
     }
 }

 <span class="kw">impl</span>&lt;I&gt; PutBack&lt;I&gt;
     <span class="kw">where </span>I: Iterator
 {
     <span class="doccomment">/// put back value `value` (builder method)
     </span><span class="kw">pub fn </span>with_value(<span class="kw-2">mut </span><span class="self">self</span>, value: I::Item) -&gt; <span class="self">Self </span>{
         <span class="self">self</span>.put_back(value);
         <span class="self">self
     </span>}

     <span class="doccomment">/// Split the `PutBack` into its parts.
     </span><span class="attribute">#[inline]
     </span><span class="kw">pub fn </span>into_parts(<span class="self">self</span>) -&gt; (<span class="prelude-ty">Option</span>&lt;I::Item&gt;, I) {
         <span class="kw">let </span>PutBack{top, iter} = <span class="self">self</span>;
         (top, iter)
     }

     <span class="doccomment">/// Put back a single value to the front of the iterator.
     ///
     /// If a value is already in the put back slot, it is overwritten.
     </span><span class="attribute">#[inline]
     </span><span class="kw">pub fn </span>put_back(<span class="kw-2">&amp;mut </span><span class="self">self</span>, x: I::Item) {
         <span class="self">self</span>.top = <span class="prelude-val">Some</span>(x);
     }
 }

 <span class="kw">impl</span>&lt;I&gt; Iterator <span class="kw">for </span>PutBack&lt;I&gt;
     <span class="kw">where </span>I: Iterator
 {
     <span class="kw">type </span>Item = I::Item;
     <span class="attribute">#[inline]
     </span><span class="kw">fn </span>next(<span class="kw-2">&amp;mut </span><span class="self">self</span>) -&gt; <span class="prelude-ty">Option</span>&lt;<span class="self">Self</span>::Item&gt; {
         <span class="kw">match </span><span class="self">self</span>.top {
             <span class="prelude-val">None </span>=&gt; <span class="self">self</span>.iter.next(),
             <span class="kw-2">ref mut </span>some =&gt; some.take(),
         }
     }
     <span class="attribute">#[inline]
     </span><span class="kw">fn </span>size_hint(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; (usize, <span class="prelude-ty">Option</span>&lt;usize&gt;) {
         <span class="comment">// Not ExactSizeIterator because size may be larger than usize
         </span>size_hint::add_scalar(<span class="self">self</span>.iter.size_hint(), <span class="self">self</span>.top.is_some() <span class="kw">as </span>usize)
     }

     <span class="kw">fn </span>count(<span class="self">self</span>) -&gt; usize {
         <span class="self">self</span>.iter.count() + (<span class="self">self</span>.top.is_some() <span class="kw">as </span>usize)
     }

     <span class="kw">fn </span>last(<span class="self">self</span>) -&gt; <span class="prelude-ty">Option</span>&lt;<span class="self">Self</span>::Item&gt; {
         <span class="self">self</span>.iter.last().or(<span class="self">self</span>.top)
     }

     <span class="kw">fn </span>nth(<span class="kw-2">&amp;mut </span><span class="self">self</span>, n: usize) -&gt; <span class="prelude-ty">Option</span>&lt;<span class="self">Self</span>::Item&gt; {
         <span class="kw">match </span><span class="self">self</span>.top {
             <span class="prelude-val">None </span>=&gt; <span class="self">self</span>.iter.nth(n),
             <span class="kw-2">ref mut </span>some =&gt; {
                 <span class="kw">if </span>n == <span class="number">0 </span>{
                     some.take()
                 } <span class="kw">else </span>{
                     <span class="kw-2">*</span>some = <span class="prelude-val">None</span>;
                     <span class="self">self</span>.iter.nth(n - <span class="number">1</span>)
                 }
             }
         }
     }

     <span class="kw">fn </span>all&lt;G&gt;(<span class="kw-2">&amp;mut </span><span class="self">self</span>, <span class="kw-2">mut </span>f: G) -&gt; bool
         <span class="kw">where </span>G: FnMut(<span class="self">Self</span>::Item) -&gt; bool
     {
         <span class="kw">if let </span><span class="prelude-val">Some</span>(elt) = <span class="self">self</span>.top.take() {
             <span class="kw">if </span>!f(elt) {
                 <span class="kw">return </span><span class="bool-val">false</span>;
             }
         }
         <span class="self">self</span>.iter.all(f)
     }

     <span class="kw">fn </span>fold&lt;Acc, G&gt;(<span class="kw-2">mut </span><span class="self">self</span>, init: Acc, <span class="kw-2">mut </span>f: G) -&gt; Acc
         <span class="kw">where </span>G: FnMut(Acc, <span class="self">Self</span>::Item) -&gt; Acc,
     {
         <span class="kw">let </span><span class="kw-2">mut </span>accum = init;
         <span class="kw">if let </span><span class="prelude-val">Some</span>(elt) = <span class="self">self</span>.top.take() {
             accum = f(accum, elt);
         }
         <span class="self">self</span>.iter.fold(accum, f)
     }
 }

 <span class="attribute">#[derive(Debug, Clone)]
 </span><span class="doccomment">/// An iterator adaptor that iterates over the cartesian product of
 /// the element sets of two iterators `I` and `J`.
 ///
 /// Iterator element type is `(I::Item, J::Item)`.
 ///
 /// See [`.cartesian_product()`](crate::Itertools::cartesian_product) for more information.
 </span><span class="attribute">#[must_use = <span class="string">&quot;iterator adaptors are lazy and do nothing unless consumed&quot;</span>]
 </span><span class="kw">pub struct </span>Product&lt;I, J&gt;
     <span class="kw">where </span>I: Iterator
 {
     a: I,
     a_cur: <span class="prelude-ty">Option</span>&lt;I::Item&gt;,
     b: J,
     b_orig: J,
 }

 <span class="doccomment">/// Create a new cartesian product iterator
 ///
 /// Iterator element type is `(I::Item, J::Item)`.
 </span><span class="kw">pub fn </span>cartesian_product&lt;I, J&gt;(<span class="kw-2">mut </span>i: I, j: J) -&gt; Product&lt;I, J&gt;
     <span class="kw">where </span>I: Iterator,
           J: Clone + Iterator,
           I::Item: Clone
 {
     Product {
         a_cur: i.next(),
         a: i,
         b: j.clone(),
         b_orig: j,
     }
 }

 <span class="kw">impl</span>&lt;I, J&gt; Iterator <span class="kw">for </span>Product&lt;I, J&gt;
     <span class="kw">where </span>I: Iterator,
           J: Clone + Iterator,
           I::Item: Clone
 {
     <span class="kw">type </span>Item = (I::Item, J::Item);

     <span class="kw">fn </span>next(<span class="kw-2">&amp;mut </span><span class="self">self</span>) -&gt; <span class="prelude-ty">Option</span>&lt;<span class="self">Self</span>::Item&gt; {
         <span class="kw">let </span>elt_b = <span class="kw">match </span><span class="self">self</span>.b.next() {
             <span class="prelude-val">None </span>=&gt; {
                 <span class="self">self</span>.b = <span class="self">self</span>.b_orig.clone();
                 <span class="kw">match </span><span class="self">self</span>.b.next() {
                     <span class="prelude-val">None </span>=&gt; <span class="kw">return </span><span class="prelude-val">None</span>,
                     <span class="prelude-val">Some</span>(x) =&gt; {
                         <span class="self">self</span>.a_cur = <span class="self">self</span>.a.next();
                         x
                     }
                 }
             }
             <span class="prelude-val">Some</span>(x) =&gt; x
         };
         <span class="self">self</span>.a_cur.as_ref().map(|a| (a.clone(), elt_b))
     }

     <span class="kw">fn </span>size_hint(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; (usize, <span class="prelude-ty">Option</span>&lt;usize&gt;) {
         <span class="kw">let </span>has_cur = <span class="self">self</span>.a_cur.is_some() <span class="kw">as </span>usize;
         <span class="comment">// Not ExactSizeIterator because size may be larger than usize
         </span><span class="kw">let </span>(b_min, b_max) = <span class="self">self</span>.b.size_hint();

         <span class="comment">// Compute a * b_orig + b for both lower and upper bound
         </span>size_hint::add(
             size_hint::mul(<span class="self">self</span>.a.size_hint(), <span class="self">self</span>.b_orig.size_hint()),
             (b_min * has_cur, b_max.map(<span class="kw">move </span>|x| x * has_cur)))
     }

     <span class="kw">fn </span>fold&lt;Acc, G&gt;(<span class="kw-2">mut </span><span class="self">self</span>, <span class="kw-2">mut </span>accum: Acc, <span class="kw-2">mut </span>f: G) -&gt; Acc
         <span class="kw">where </span>G: FnMut(Acc, <span class="self">Self</span>::Item) -&gt; Acc,
     {
         <span class="comment">// use a split loop to handle the loose a_cur as well as avoiding to
         // clone b_orig at the end.
         </span><span class="kw">if let </span><span class="prelude-val">Some</span>(<span class="kw-2">mut </span>a) = <span class="self">self</span>.a_cur.take() {
             <span class="kw">let </span><span class="kw-2">mut </span>b = <span class="self">self</span>.b;
             <span class="kw">loop </span>{
                 accum = b.fold(accum, |acc, elt| f(acc, (a.clone(), elt)));

                 <span class="comment">// we can only continue iterating a if we had a first element;
                 </span><span class="kw">if let </span><span class="prelude-val">Some</span>(next_a) = <span class="self">self</span>.a.next() {
                     b = <span class="self">self</span>.b_orig.clone();
                     a = next_a;
                 } <span class="kw">else </span>{
                     <span class="kw">break</span>;
                 }
             }
         }
         accum
     }
 }

 <span class="kw">impl</span>&lt;I, J&gt; FusedIterator <span class="kw">for </span>Product&lt;I, J&gt;
     <span class="kw">where </span>I: FusedIterator,
           J: Clone + FusedIterator,
           I::Item: Clone
 {}

 <span class="doccomment">/// A “meta iterator adaptor”. Its closure receives a reference to the iterator
 /// and may pick off as many elements as it likes, to produce the next iterator element.
 ///
 /// Iterator element type is *X*, if the return type of `F` is *Option\&lt;X\&gt;*.
 ///
 /// See [`.batching()`](crate::Itertools::batching) for more information.
 </span><span class="attribute">#[derive(Clone)]
 #[must_use = <span class="string">&quot;iterator adaptors are lazy and do nothing unless consumed&quot;</span>]
 </span><span class="kw">pub struct </span>Batching&lt;I, F&gt; {
     f: F,
     iter: I,
 }

 <span class="kw">impl</span>&lt;I, F&gt; fmt::Debug <span class="kw">for </span>Batching&lt;I, F&gt; <span class="kw">where </span>I: fmt::Debug {
     <span class="macro">debug_fmt_fields!</span>(Batching, iter);
 }

 <span class="doccomment">/// Create a new Batching iterator.
 </span><span class="kw">pub fn </span>batching&lt;I, F&gt;(iter: I, f: F) -&gt; Batching&lt;I, F&gt; {
     Batching { f, iter }
 }

 <span class="kw">impl</span>&lt;B, F, I&gt; Iterator <span class="kw">for </span>Batching&lt;I, F&gt;
     <span class="kw">where </span>I: Iterator,
           F: FnMut(<span class="kw-2">&amp;mut </span>I) -&gt; <span class="prelude-ty">Option</span>&lt;B&gt;
 {
     <span class="kw">type </span>Item = B;
     <span class="attribute">#[inline]
     </span><span class="kw">fn </span>next(<span class="kw-2">&amp;mut </span><span class="self">self</span>) -&gt; <span class="prelude-ty">Option</span>&lt;<span class="self">Self</span>::Item&gt; {
         (<span class="self">self</span>.f)(<span class="kw-2">&amp;mut </span><span class="self">self</span>.iter)
     }
 }

 <span class="doccomment">/// An iterator adaptor that steps a number elements in the base iterator
 /// for each iteration.
 ///
 /// The iterator steps by yielding the next element from the base iterator,
 /// then skipping forward *n-1* elements.
 ///
 /// See [`.step()`](crate::Itertools::step) for more information.
 </span><span class="attribute">#[deprecated(note=<span class="string">&quot;Use std .step_by() instead&quot;</span>, since=<span class="string">&quot;0.8.0&quot;</span>)]
 #[allow(deprecated)]
 #[derive(Clone, Debug)]
 #[must_use = <span class="string">&quot;iterator adaptors are lazy and do nothing unless consumed&quot;</span>]
 </span><span class="kw">pub struct </span>Step&lt;I&gt; {
     iter: Fuse&lt;I&gt;,
     skip: usize,
 }

 <span class="doccomment">/// Create a `Step` iterator.
 ///
 /// **Panics** if the step is 0.
 </span><span class="attribute">#[allow(deprecated)]
 </span><span class="kw">pub fn </span>step&lt;I&gt;(iter: I, step: usize) -&gt; Step&lt;I&gt;
     <span class="kw">where </span>I: Iterator
 {
     <span class="macro">assert!</span>(step != <span class="number">0</span>);
     Step {
         iter: iter.fuse(),
         skip: step - <span class="number">1</span>,
     }
 }

 <span class="attribute">#[allow(deprecated)]
 </span><span class="kw">impl</span>&lt;I&gt; Iterator <span class="kw">for </span>Step&lt;I&gt;
     <span class="kw">where </span>I: Iterator
 {
     <span class="kw">type </span>Item = I::Item;
     <span class="attribute">#[inline]
     </span><span class="kw">fn </span>next(<span class="kw-2">&amp;mut </span><span class="self">self</span>) -&gt; <span class="prelude-ty">Option</span>&lt;<span class="self">Self</span>::Item&gt; {
         <span class="kw">let </span>elt = <span class="self">self</span>.iter.next();
         <span class="kw">if </span><span class="self">self</span>.skip &gt; <span class="number">0 </span>{
             <span class="self">self</span>.iter.nth(<span class="self">self</span>.skip - <span class="number">1</span>);
         }
         elt
     }

     <span class="kw">fn </span>size_hint(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; (usize, <span class="prelude-ty">Option</span>&lt;usize&gt;) {
         <span class="kw">let </span>(low, high) = <span class="self">self</span>.iter.size_hint();
         <span class="kw">let </span>div = |x: usize| {
             <span class="kw">if </span>x == <span class="number">0 </span>{
                 <span class="number">0
             </span>} <span class="kw">else </span>{
                 <span class="number">1 </span>+ (x - <span class="number">1</span>) / (<span class="self">self</span>.skip + <span class="number">1</span>)
             }
         };
         (div(low), high.map(div))
     }
 }

 <span class="comment">// known size
 </span><span class="attribute">#[allow(deprecated)]
 </span><span class="kw">impl</span>&lt;I&gt; ExactSizeIterator <span class="kw">for </span>Step&lt;I&gt;
     <span class="kw">where </span>I: ExactSizeIterator
 {}

 <span class="kw">pub trait </span>MergePredicate&lt;T&gt; {
     <span class="kw">fn </span>merge_pred(<span class="kw-2">&amp;mut </span><span class="self">self</span>, a: <span class="kw-2">&amp;</span>T, b: <span class="kw-2">&amp;</span>T) -&gt; bool;
 }

 <span class="attribute">#[derive(Clone, Debug)]
 </span><span class="kw">pub struct </span>MergeLte;

 <span class="kw">impl</span>&lt;T: PartialOrd&gt; MergePredicate&lt;T&gt; <span class="kw">for </span>MergeLte {
     <span class="kw">fn </span>merge_pred(<span class="kw-2">&amp;mut </span><span class="self">self</span>, a: <span class="kw-2">&amp;</span>T, b: <span class="kw-2">&amp;</span>T) -&gt; bool {
         a &lt;= b
     }
 }

 <span class="doccomment">/// An iterator adaptor that merges the two base iterators in ascending order.
 /// If both base iterators are sorted (ascending), the result is sorted.
 ///
 /// Iterator element type is `I::Item`.
 ///
 /// See [`.merge()`](crate::Itertools::merge_by) for more information.
 </span><span class="kw">pub type </span>Merge&lt;I, J&gt; = MergeBy&lt;I, J, MergeLte&gt;;

 <span class="doccomment">/// Create an iterator that merges elements in `i` and `j`.
 ///
 /// [`IntoIterator`] enabled version of [`Itertools::merge`](crate::Itertools::merge).
 ///
 /// ```
 /// use itertools::merge;
 ///
 /// for elt in merge(&amp;[1, 2, 3], &amp;[2, 3, 4]) {
 ///     /* loop body */
 /// }
 /// ```
 </span><span class="kw">pub fn </span>merge&lt;I, J&gt;(i: I, j: J) -&gt; Merge&lt;&lt;I <span class="kw">as </span>IntoIterator&gt;::IntoIter, &lt;J <span class="kw">as </span>IntoIterator&gt;::IntoIter&gt;
     <span class="kw">where </span>I: IntoIterator,
           J: IntoIterator&lt;Item = I::Item&gt;,
           I::Item: PartialOrd
 {
     merge_by_new(i, j, MergeLte)
 }

 <span class="doccomment">/// An iterator adaptor that merges the two base iterators in ascending order.
 /// If both base iterators are sorted (ascending), the result is sorted.
 ///
 /// Iterator element type is `I::Item`.
 ///
 /// See [`.merge_by()`](crate::Itertools::merge_by) for more information.
 </span><span class="attribute">#[must_use = <span class="string">&quot;iterator adaptors are lazy and do nothing unless consumed&quot;</span>]
 </span><span class="kw">pub struct </span>MergeBy&lt;I, J, F&gt;
     <span class="kw">where </span>I: Iterator,
           J: Iterator&lt;Item = I::Item&gt;
 {
     a: Peekable&lt;I&gt;,
     b: Peekable&lt;J&gt;,
     fused: <span class="prelude-ty">Option</span>&lt;bool&gt;,
     cmp: F,
 }

 <span class="kw">impl</span>&lt;I, J, F&gt; fmt::Debug <span class="kw">for </span>MergeBy&lt;I, J, F&gt;
     <span class="kw">where </span>I: Iterator + fmt::Debug, J: Iterator&lt;Item = I::Item&gt; + fmt::Debug,
           I::Item: fmt::Debug,
 {
     <span class="macro">debug_fmt_fields!</span>(MergeBy, a, b);
 }

 <span class="kw">impl</span>&lt;T, F: FnMut(<span class="kw-2">&amp;</span>T, <span class="kw-2">&amp;</span>T)-&gt;bool&gt; MergePredicate&lt;T&gt; <span class="kw">for </span>F {
     <span class="kw">fn </span>merge_pred(<span class="kw-2">&amp;mut </span><span class="self">self</span>, a: <span class="kw-2">&amp;</span>T, b: <span class="kw-2">&amp;</span>T) -&gt; bool {
         <span class="self">self</span>(a, b)
     }
 }

 <span class="doccomment">/// Create a `MergeBy` iterator.
 </span><span class="kw">pub fn </span>merge_by_new&lt;I, J, F&gt;(a: I, b: J, cmp: F) -&gt; MergeBy&lt;I::IntoIter, J::IntoIter, F&gt;
     <span class="kw">where </span>I: IntoIterator,
           J: IntoIterator&lt;Item = I::Item&gt;,
           F: MergePredicate&lt;I::Item&gt;,
 {
     MergeBy {
         a: a.into_iter().peekable(),
         b: b.into_iter().peekable(),
         fused: <span class="prelude-val">None</span>,
         cmp,
     }
 }

 <span class="kw">impl</span>&lt;I, J, F&gt; Clone <span class="kw">for </span>MergeBy&lt;I, J, F&gt;
     <span class="kw">where </span>I: Iterator,
           J: Iterator&lt;Item = I::Item&gt;,
           Peekable&lt;I&gt;: Clone,
           Peekable&lt;J&gt;: Clone,
           F: Clone
 {
     <span class="macro">clone_fields!</span>(a, b, fused, cmp);
 }

 <span class="kw">impl</span>&lt;I, J, F&gt; Iterator <span class="kw">for </span>MergeBy&lt;I, J, F&gt;
     <span class="kw">where </span>I: Iterator,
           J: Iterator&lt;Item = I::Item&gt;,
           F: MergePredicate&lt;I::Item&gt;
 {
     <span class="kw">type </span>Item = I::Item;

     <span class="kw">fn </span>next(<span class="kw-2">&amp;mut </span><span class="self">self</span>) -&gt; <span class="prelude-ty">Option</span>&lt;<span class="self">Self</span>::Item&gt; {
         <span class="kw">let </span>less_than = <span class="kw">match </span><span class="self">self</span>.fused {
             <span class="prelude-val">Some</span>(lt) =&gt; lt,
             <span class="prelude-val">None </span>=&gt; <span class="kw">match </span>(<span class="self">self</span>.a.peek(), <span class="self">self</span>.b.peek()) {
                 (<span class="prelude-val">Some</span>(a), <span class="prelude-val">Some</span>(b)) =&gt; <span class="self">self</span>.cmp.merge_pred(a, b),
                 (<span class="prelude-val">Some</span>(<span class="kw">_</span>), <span class="prelude-val">None</span>) =&gt; {
                     <span class="self">self</span>.fused = <span class="prelude-val">Some</span>(<span class="bool-val">true</span>);
                     <span class="bool-val">true
                 </span>}
                 (<span class="prelude-val">None</span>, <span class="prelude-val">Some</span>(<span class="kw">_</span>)) =&gt; {
                     <span class="self">self</span>.fused = <span class="prelude-val">Some</span>(<span class="bool-val">false</span>);
                     <span class="bool-val">false
                 </span>}
                 (<span class="prelude-val">None</span>, <span class="prelude-val">None</span>) =&gt; <span class="kw">return </span><span class="prelude-val">None</span>,
             }
         };
         <span class="kw">if </span>less_than {
             <span class="self">self</span>.a.next()
         } <span class="kw">else </span>{
             <span class="self">self</span>.b.next()
         }
     }

     <span class="kw">fn </span>size_hint(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; (usize, <span class="prelude-ty">Option</span>&lt;usize&gt;) {
         <span class="comment">// Not ExactSizeIterator because size may be larger than usize
         </span>size_hint::add(<span class="self">self</span>.a.size_hint(), <span class="self">self</span>.b.size_hint())
     }
 }

 <span class="kw">impl</span>&lt;I, J, F&gt; FusedIterator <span class="kw">for </span>MergeBy&lt;I, J, F&gt;
     <span class="kw">where </span>I: FusedIterator,
           J: FusedIterator&lt;Item = I::Item&gt;,
           F: MergePredicate&lt;I::Item&gt;
 {}

 <span class="doccomment">/// An iterator adaptor that borrows from a `Clone`-able iterator
 /// to only pick off elements while the predicate returns `true`.
 ///
 /// See [`.take_while_ref()`](crate::Itertools::take_while_ref) for more information.
 </span><span class="attribute">#[must_use = <span class="string">&quot;iterator adaptors are lazy and do nothing unless consumed&quot;</span>]
 </span><span class="kw">pub struct </span>TakeWhileRef&lt;<span class="lifetime">&#39;a</span>, I: <span class="lifetime">&#39;a</span>, F&gt; {
     iter: <span class="kw-2">&amp;</span><span class="lifetime">&#39;a </span><span class="kw-2">mut </span>I,
     f: F,
 }

 <span class="kw">impl</span>&lt;<span class="lifetime">&#39;a</span>, I, F&gt; fmt::Debug <span class="kw">for </span>TakeWhileRef&lt;<span class="lifetime">&#39;a</span>, I, F&gt;
     <span class="kw">where </span>I: Iterator + fmt::Debug,
 {
     <span class="macro">debug_fmt_fields!</span>(TakeWhileRef, iter);
 }

 <span class="doccomment">/// Create a new `TakeWhileRef` from a reference to clonable iterator.
 </span><span class="kw">pub fn </span>take_while_ref&lt;I, F&gt;(iter: <span class="kw-2">&amp;mut </span>I, f: F) -&gt; TakeWhileRef&lt;I, F&gt;
     <span class="kw">where </span>I: Iterator + Clone
 {
     TakeWhileRef { iter, f }
 }

 <span class="kw">impl</span>&lt;<span class="lifetime">&#39;a</span>, I, F&gt; Iterator <span class="kw">for </span>TakeWhileRef&lt;<span class="lifetime">&#39;a</span>, I, F&gt;
     <span class="kw">where </span>I: Iterator + Clone,
           F: FnMut(<span class="kw-2">&amp;</span>I::Item) -&gt; bool
 {
     <span class="kw">type </span>Item = I::Item;

     <span class="kw">fn </span>next(<span class="kw-2">&amp;mut </span><span class="self">self</span>) -&gt; <span class="prelude-ty">Option</span>&lt;<span class="self">Self</span>::Item&gt; {
         <span class="kw">let </span>old = <span class="self">self</span>.iter.clone();
         <span class="kw">match </span><span class="self">self</span>.iter.next() {
             <span class="prelude-val">None </span>=&gt; <span class="prelude-val">None</span>,
             <span class="prelude-val">Some</span>(elt) =&gt; {
                 <span class="kw">if </span>(<span class="self">self</span>.f)(<span class="kw-2">&amp;</span>elt) {
                     <span class="prelude-val">Some</span>(elt)
                 } <span class="kw">else </span>{
                     <span class="kw-2">*</span><span class="self">self</span>.iter = old;
                     <span class="prelude-val">None
                 </span>}
             }
         }
     }

     <span class="kw">fn </span>size_hint(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; (usize, <span class="prelude-ty">Option</span>&lt;usize&gt;) {
         (<span class="number">0</span>, <span class="self">self</span>.iter.size_hint().<span class="number">1</span>)
     }
 }

 <span class="doccomment">/// An iterator adaptor that filters `Option&lt;A&gt;` iterator elements
 /// and produces `A`. Stops on the first `None` encountered.
 ///
 /// See [`.while_some()`](crate::Itertools::while_some) for more information.
 </span><span class="attribute">#[derive(Clone, Debug)]
 #[must_use = <span class="string">&quot;iterator adaptors are lazy and do nothing unless consumed&quot;</span>]
 </span><span class="kw">pub struct </span>WhileSome&lt;I&gt; {
     iter: I,
 }

 <span class="doccomment">/// Create a new `WhileSome&lt;I&gt;`.
 </span><span class="kw">pub fn </span>while_some&lt;I&gt;(iter: I) -&gt; WhileSome&lt;I&gt; {
     WhileSome { iter }
 }

 <span class="kw">impl</span>&lt;I, A&gt; Iterator <span class="kw">for </span>WhileSome&lt;I&gt;
     <span class="kw">where </span>I: Iterator&lt;Item = <span class="prelude-ty">Option</span>&lt;A&gt;&gt;
 {
     <span class="kw">type </span>Item = A;

     <span class="kw">fn </span>next(<span class="kw-2">&amp;mut </span><span class="self">self</span>) -&gt; <span class="prelude-ty">Option</span>&lt;<span class="self">Self</span>::Item&gt; {
         <span class="kw">match </span><span class="self">self</span>.iter.next() {
             <span class="prelude-val">None </span>| <span class="prelude-val">Some</span>(<span class="prelude-val">None</span>) =&gt; <span class="prelude-val">None</span>,
             <span class="prelude-val">Some</span>(elt) =&gt; elt,
         }
     }

     <span class="kw">fn </span>size_hint(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; (usize, <span class="prelude-ty">Option</span>&lt;usize&gt;) {
         (<span class="number">0</span>, <span class="self">self</span>.iter.size_hint().<span class="number">1</span>)
     }
 }

 <span class="doccomment">/// An iterator to iterate through all combinations in a `Clone`-able iterator that produces tuples
 /// of a specific size.
 ///
 /// See [`.tuple_combinations()`](crate::Itertools::tuple_combinations) for more
 /// information.
 </span><span class="attribute">#[derive(Clone, Debug)]
 #[must_use = <span class="string">&quot;iterator adaptors are lazy and do nothing unless consumed&quot;</span>]
 </span><span class="kw">pub struct </span>TupleCombinations&lt;I, T&gt;
     <span class="kw">where </span>I: Iterator,
           T: HasCombination&lt;I&gt;
 {
     iter: T::Combination,
     _mi: PhantomData&lt;I&gt;,
 }

 <span class="kw">pub trait </span>HasCombination&lt;I&gt;: Sized {
     <span class="kw">type </span>Combination: From&lt;I&gt; + Iterator&lt;Item = <span class="self">Self</span>&gt;;
 }

 <span class="doccomment">/// Create a new `TupleCombinations` from a clonable iterator.
 </span><span class="kw">pub fn </span>tuple_combinations&lt;T, I&gt;(iter: I) -&gt; TupleCombinations&lt;I, T&gt;
     <span class="kw">where </span>I: Iterator + Clone,
           I::Item: Clone,
           T: HasCombination&lt;I&gt;,
 {
     TupleCombinations {
         iter: T::Combination::from(iter),
         _mi: PhantomData,
     }
 }

 <span class="kw">impl</span>&lt;I, T&gt; Iterator <span class="kw">for </span>TupleCombinations&lt;I, T&gt;
     <span class="kw">where </span>I: Iterator,
           T: HasCombination&lt;I&gt;,
 {
     <span class="kw">type </span>Item = T;

     <span class="kw">fn </span>next(<span class="kw-2">&amp;mut </span><span class="self">self</span>) -&gt; <span class="prelude-ty">Option</span>&lt;<span class="self">Self</span>::Item&gt; {
         <span class="self">self</span>.iter.next()
     }
 }

 <span class="kw">impl</span>&lt;I, T&gt; FusedIterator <span class="kw">for </span>TupleCombinations&lt;I, T&gt;
     <span class="kw">where </span>I: FusedIterator,
           T: HasCombination&lt;I&gt;,
 {}

 <span class="attribute">#[derive(Clone, Debug)]
 </span><span class="kw">pub struct </span>Tuple1Combination&lt;I&gt; {
     iter: I,
 }

 <span class="kw">impl</span>&lt;I&gt; From&lt;I&gt; <span class="kw">for </span>Tuple1Combination&lt;I&gt; {
     <span class="kw">fn </span>from(iter: I) -&gt; <span class="self">Self </span>{
         Tuple1Combination { iter }
     }
 }

 <span class="kw">impl</span>&lt;I: Iterator&gt; Iterator <span class="kw">for </span>Tuple1Combination&lt;I&gt; {
     <span class="kw">type </span>Item = (I::Item,);

     <span class="kw">fn </span>next(<span class="kw-2">&amp;mut </span><span class="self">self</span>) -&gt; <span class="prelude-ty">Option</span>&lt;<span class="self">Self</span>::Item&gt; {
         <span class="self">self</span>.iter.next().map(|x| (x,))
     }
 }

 <span class="kw">impl</span>&lt;I: Iterator&gt; HasCombination&lt;I&gt; <span class="kw">for </span>(I::Item,) {
     <span class="kw">type </span>Combination = Tuple1Combination&lt;I&gt;;
 }

 <span class="macro">macro_rules! </span>impl_tuple_combination {
     (<span class="macro-nonterminal">$C</span>:ident <span class="macro-nonterminal">$P</span>:ident ; $(<span class="macro-nonterminal">$X</span>:ident)<span class="kw-2">*</span>) =&gt; (
         <span class="attribute">#[derive(Clone, Debug)]
         </span><span class="kw">pub struct </span><span class="macro-nonterminal">$C</span>&lt;I: Iterator&gt; {
             item: <span class="prelude-ty">Option</span>&lt;I::Item&gt;,
             iter: I,
             c: <span class="macro-nonterminal">$P</span>&lt;I&gt;,
         }

         <span class="kw">impl</span>&lt;I: Iterator + Clone&gt; From&lt;I&gt; <span class="kw">for </span><span class="macro-nonterminal">$C</span>&lt;I&gt; {
             <span class="kw">fn </span>from(<span class="kw-2">mut </span>iter: I) -&gt; <span class="self">Self </span>{
                 <span class="self">Self </span>{
                     item: iter.next(),
                     iter: iter.clone(),
                     c: iter.into(),
                 }
             }
         }

         <span class="kw">impl</span>&lt;I: Iterator + Clone&gt; From&lt;I&gt; <span class="kw">for </span><span class="macro-nonterminal">$C</span>&lt;Fuse&lt;I&gt;&gt; {
             <span class="kw">fn </span>from(iter: I) -&gt; <span class="self">Self </span>{
                 <span class="self">Self</span>::from(iter.fuse())
             }
         }

         <span class="kw">impl</span>&lt;I, A&gt; Iterator <span class="kw">for </span><span class="macro-nonterminal">$C</span>&lt;I&gt;
             <span class="kw">where </span>I: Iterator&lt;Item = A&gt; + Clone,
                   I::Item: Clone
         {
             <span class="kw">type </span>Item = (A, $(<span class="macro">ignore_ident!</span>(<span class="macro-nonterminal">$X</span>, A)),<span class="kw-2">*</span>);

             <span class="kw">fn </span>next(<span class="kw-2">&amp;mut </span><span class="self">self</span>) -&gt; <span class="prelude-ty">Option</span>&lt;<span class="self">Self</span>::Item&gt; {
                 <span class="kw">if let </span><span class="prelude-val">Some</span>(($(<span class="macro-nonterminal">$X</span>),<span class="kw-2">*</span>,)) = <span class="self">self</span>.c.next() {
                     <span class="kw">let </span>z = <span class="self">self</span>.item.clone().unwrap();
                     <span class="prelude-val">Some</span>((z, $(<span class="macro-nonterminal">$X</span>),<span class="kw-2">*</span>))
                 } <span class="kw">else </span>{
                     <span class="self">self</span>.item = <span class="self">self</span>.iter.next();
                     <span class="self">self</span>.item.clone().and_then(|z| {
                         <span class="self">self</span>.c = <span class="self">self</span>.iter.clone().into();
                         <span class="self">self</span>.c.next().map(|($(<span class="macro-nonterminal">$X</span>),<span class="kw-2">*</span>,)| (z, $(<span class="macro-nonterminal">$X</span>),<span class="kw-2">*</span>))
                     })
                 }
             }
         }

         <span class="kw">impl</span>&lt;I, A&gt; HasCombination&lt;I&gt; <span class="kw">for </span>(A, $(<span class="macro">ignore_ident!</span>(<span class="macro-nonterminal">$X</span>, A)),<span class="kw-2">*</span>)
             <span class="kw">where </span>I: Iterator&lt;Item = A&gt; + Clone,
                   I::Item: Clone
         {
             <span class="kw">type </span>Combination = <span class="macro-nonterminal">$C</span>&lt;Fuse&lt;I&gt;&gt;;
         }
     )
 }

 <span class="comment">// This snippet generates the twelve `impl_tuple_combination!` invocations:
 //    use core::iter;
 //    use itertools::Itertools;
 //
 //    for i in 2..=12 {
 //        println!(&quot;impl_tuple_combination!(Tuple{arity}Combination Tuple{prev}Combination; {idents});&quot;,
 //            arity = i,
 //            prev = i - 1,
 //            idents = (&#39;a&#39;..&#39;z&#39;).take(i - 1).join(&quot; &quot;),
 //        );
 //    }
 // It could probably be replaced by a bit more macro cleverness.
 </span><span class="macro">impl_tuple_combination!</span>(Tuple2Combination Tuple1Combination; a);
 <span class="macro">impl_tuple_combination!</span>(Tuple3Combination Tuple2Combination; a b);
 <span class="macro">impl_tuple_combination!</span>(Tuple4Combination Tuple3Combination; a b c);
 <span class="macro">impl_tuple_combination!</span>(Tuple5Combination Tuple4Combination; a b c d);
 <span class="macro">impl_tuple_combination!</span>(Tuple6Combination Tuple5Combination; a b c d e);
 <span class="macro">impl_tuple_combination!</span>(Tuple7Combination Tuple6Combination; a b c d e f);
 <span class="macro">impl_tuple_combination!</span>(Tuple8Combination Tuple7Combination; a b c d e f g);
 <span class="macro">impl_tuple_combination!</span>(Tuple9Combination Tuple8Combination; a b c d e f g h);
 <span class="macro">impl_tuple_combination!</span>(Tuple10Combination Tuple9Combination; a b c d e f g h i);
 <span class="macro">impl_tuple_combination!</span>(Tuple11Combination Tuple10Combination; a b c d e f g h i j);
 <span class="macro">impl_tuple_combination!</span>(Tuple12Combination Tuple11Combination; a b c d e f g h i j k);

 <span class="doccomment">/// An iterator adapter to filter values within a nested `Result::Ok`.
 ///
 /// See [`.filter_ok()`](crate::Itertools::filter_ok) for more information.
 </span><span class="attribute">#[derive(Clone)]
 #[must_use = <span class="string">&quot;iterator adaptors are lazy and do nothing unless consumed&quot;</span>]
 </span><span class="kw">pub struct </span>FilterOk&lt;I, F&gt; {
     iter: I,
     f: F
 }

 <span class="kw">impl</span>&lt;I, F&gt; fmt::Debug <span class="kw">for </span>FilterOk&lt;I, F&gt;
 <span class="kw">where
     </span>I: fmt::Debug,
 {
     <span class="macro">debug_fmt_fields!</span>(FilterOk, iter);
 }

 <span class="doccomment">/// Create a new `FilterOk` iterator.
 </span><span class="kw">pub fn </span>filter_ok&lt;I, F, T, E&gt;(iter: I, f: F) -&gt; FilterOk&lt;I, F&gt;
     <span class="kw">where </span>I: Iterator&lt;Item = <span class="prelude-ty">Result</span>&lt;T, E&gt;&gt;,
           F: FnMut(<span class="kw-2">&amp;</span>T) -&gt; bool,
 {
     FilterOk {
         iter,
         f,
     }
 }

 <span class="kw">impl</span>&lt;I, F, T, E&gt; Iterator <span class="kw">for </span>FilterOk&lt;I, F&gt;
     <span class="kw">where </span>I: Iterator&lt;Item = <span class="prelude-ty">Result</span>&lt;T, E&gt;&gt;,
           F: FnMut(<span class="kw-2">&amp;</span>T) -&gt; bool,
 {
     <span class="kw">type </span>Item = <span class="prelude-ty">Result</span>&lt;T, E&gt;;

     <span class="kw">fn </span>next(<span class="kw-2">&amp;mut </span><span class="self">self</span>) -&gt; <span class="prelude-ty">Option</span>&lt;<span class="self">Self</span>::Item&gt; {
         <span class="kw">loop </span>{
             <span class="kw">match </span><span class="self">self</span>.iter.next() {
                 <span class="prelude-val">Some</span>(<span class="prelude-val">Ok</span>(v)) =&gt; {
                     <span class="kw">if </span>(<span class="self">self</span>.f)(<span class="kw-2">&amp;</span>v) {
                         <span class="kw">return </span><span class="prelude-val">Some</span>(<span class="prelude-val">Ok</span>(v));
                     }
                 },
                 <span class="prelude-val">Some</span>(<span class="prelude-val">Err</span>(e)) =&gt; <span class="kw">return </span><span class="prelude-val">Some</span>(<span class="prelude-val">Err</span>(e)),
                 <span class="prelude-val">None </span>=&gt; <span class="kw">return </span><span class="prelude-val">None</span>,
             }
         }
     }

     <span class="kw">fn </span>size_hint(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; (usize, <span class="prelude-ty">Option</span>&lt;usize&gt;) {
         (<span class="number">0</span>, <span class="self">self</span>.iter.size_hint().<span class="number">1</span>)
     }

     <span class="kw">fn </span>fold&lt;Acc, Fold&gt;(<span class="self">self</span>, init: Acc, fold_f: Fold) -&gt; Acc
         <span class="kw">where </span>Fold: FnMut(Acc, <span class="self">Self</span>::Item) -&gt; Acc,
     {
         <span class="kw">let </span><span class="kw-2">mut </span>f = <span class="self">self</span>.f;
         <span class="self">self</span>.iter.filter(|v| {
             v.as_ref().map(<span class="kw-2">&amp;mut </span>f).unwrap_or(<span class="bool-val">true</span>)
         }).fold(init, fold_f)
     }

     <span class="kw">fn </span>collect&lt;C&gt;(<span class="self">self</span>) -&gt; C
         <span class="kw">where </span>C: FromIterator&lt;<span class="self">Self</span>::Item&gt;
     {
         <span class="kw">let </span><span class="kw-2">mut </span>f = <span class="self">self</span>.f;
         <span class="self">self</span>.iter.filter(|v| {
             v.as_ref().map(<span class="kw-2">&amp;mut </span>f).unwrap_or(<span class="bool-val">true</span>)
         }).collect()
     }
 }

 <span class="kw">impl</span>&lt;I, F, T, E&gt; FusedIterator <span class="kw">for </span>FilterOk&lt;I, F&gt;
     <span class="kw">where </span>I: FusedIterator&lt;Item = <span class="prelude-ty">Result</span>&lt;T, E&gt;&gt;,
           F: FnMut(<span class="kw-2">&amp;</span>T) -&gt; bool,
 {}

 <span class="doccomment">/// An iterator adapter to filter and apply a transformation on values within a nested `Result::Ok`.
 ///
 /// See [`.filter_map_ok()`](crate::Itertools::filter_map_ok) for more information.
 </span><span class="attribute">#[must_use = <span class="string">&quot;iterator adaptors are lazy and do nothing unless consumed&quot;</span>]
 </span><span class="kw">pub struct </span>FilterMapOk&lt;I, F&gt; {
     iter: I,
     f: F
 }

 <span class="kw">impl</span>&lt;I, F&gt; fmt::Debug <span class="kw">for </span>FilterMapOk&lt;I, F&gt;
 <span class="kw">where
     </span>I: fmt::Debug,
 {
     <span class="macro">debug_fmt_fields!</span>(FilterMapOk, iter);
 }

 <span class="kw">fn </span>transpose_result&lt;T, E&gt;(result: <span class="prelude-ty">Result</span>&lt;<span class="prelude-ty">Option</span>&lt;T&gt;, E&gt;) -&gt; <span class="prelude-ty">Option</span>&lt;<span class="prelude-ty">Result</span>&lt;T, E&gt;&gt; {
     <span class="kw">match </span>result {
         <span class="prelude-val">Ok</span>(<span class="prelude-val">Some</span>(v)) =&gt; <span class="prelude-val">Some</span>(<span class="prelude-val">Ok</span>(v)),
         <span class="prelude-val">Ok</span>(<span class="prelude-val">None</span>) =&gt; <span class="prelude-val">None</span>,
         <span class="prelude-val">Err</span>(e) =&gt; <span class="prelude-val">Some</span>(<span class="prelude-val">Err</span>(e)),
     }
 }

 <span class="doccomment">/// Create a new `FilterOk` iterator.
 </span><span class="kw">pub fn </span>filter_map_ok&lt;I, F, T, U, E&gt;(iter: I, f: F) -&gt; FilterMapOk&lt;I, F&gt;
     <span class="kw">where </span>I: Iterator&lt;Item = <span class="prelude-ty">Result</span>&lt;T, E&gt;&gt;,
           F: FnMut(T) -&gt; <span class="prelude-ty">Option</span>&lt;U&gt;,
 {
     FilterMapOk {
         iter,
         f,
     }
 }

 <span class="kw">impl</span>&lt;I, F, T, U, E&gt; Iterator <span class="kw">for </span>FilterMapOk&lt;I, F&gt;
     <span class="kw">where </span>I: Iterator&lt;Item = <span class="prelude-ty">Result</span>&lt;T, E&gt;&gt;,
           F: FnMut(T) -&gt; <span class="prelude-ty">Option</span>&lt;U&gt;,
 {
     <span class="kw">type </span>Item = <span class="prelude-ty">Result</span>&lt;U, E&gt;;

     <span class="kw">fn </span>next(<span class="kw-2">&amp;mut </span><span class="self">self</span>) -&gt; <span class="prelude-ty">Option</span>&lt;<span class="self">Self</span>::Item&gt; {
         <span class="kw">loop </span>{
             <span class="kw">match </span><span class="self">self</span>.iter.next() {
                 <span class="prelude-val">Some</span>(<span class="prelude-val">Ok</span>(v)) =&gt; {
                     <span class="kw">if let </span><span class="prelude-val">Some</span>(v) = (<span class="self">self</span>.f)(v) {
                         <span class="kw">return </span><span class="prelude-val">Some</span>(<span class="prelude-val">Ok</span>(v));
                     }
                 },
                 <span class="prelude-val">Some</span>(<span class="prelude-val">Err</span>(e)) =&gt; <span class="kw">return </span><span class="prelude-val">Some</span>(<span class="prelude-val">Err</span>(e)),
                 <span class="prelude-val">None </span>=&gt; <span class="kw">return </span><span class="prelude-val">None</span>,
             }
         }
     }

     <span class="kw">fn </span>size_hint(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; (usize, <span class="prelude-ty">Option</span>&lt;usize&gt;) {
         (<span class="number">0</span>, <span class="self">self</span>.iter.size_hint().<span class="number">1</span>)
     }

     <span class="kw">fn </span>fold&lt;Acc, Fold&gt;(<span class="self">self</span>, init: Acc, fold_f: Fold) -&gt; Acc
         <span class="kw">where </span>Fold: FnMut(Acc, <span class="self">Self</span>::Item) -&gt; Acc,
     {
         <span class="kw">let </span><span class="kw-2">mut </span>f = <span class="self">self</span>.f;
         <span class="self">self</span>.iter.filter_map(|v| {
             transpose_result(v.map(<span class="kw-2">&amp;mut </span>f))
         }).fold(init, fold_f)
     }

     <span class="kw">fn </span>collect&lt;C&gt;(<span class="self">self</span>) -&gt; C
         <span class="kw">where </span>C: FromIterator&lt;<span class="self">Self</span>::Item&gt;
     {
         <span class="kw">let </span><span class="kw-2">mut </span>f = <span class="self">self</span>.f;
         <span class="self">self</span>.iter.filter_map(|v| {
             transpose_result(v.map(<span class="kw-2">&amp;mut </span>f))
         }).collect()
     }
 }

 <span class="kw">impl</span>&lt;I, F, T, U, E&gt; FusedIterator <span class="kw">for </span>FilterMapOk&lt;I, F&gt;
     <span class="kw">where </span>I: FusedIterator&lt;Item = <span class="prelude-ty">Result</span>&lt;T, E&gt;&gt;,
           F: FnMut(T) -&gt; <span class="prelude-ty">Option</span>&lt;U&gt;,
 {}

 <span class="doccomment">/// An iterator adapter to get the positions of each element that matches a predicate.
 ///
 /// See [`.positions()`](crate::Itertools::positions) for more information.
 </span><span class="attribute">#[derive(Clone)]
 #[must_use = <span class="string">&quot;iterator adaptors are lazy and do nothing unless consumed&quot;</span>]
 </span><span class="kw">pub struct </span>Positions&lt;I, F&gt; {
     iter: I,
     f: F,
     count: usize,
 }

 <span class="kw">impl</span>&lt;I, F&gt; fmt::Debug <span class="kw">for </span>Positions&lt;I, F&gt;
 <span class="kw">where
     </span>I: fmt::Debug,
 {
     <span class="macro">debug_fmt_fields!</span>(Positions, iter, count);
 }

 <span class="doccomment">/// Create a new `Positions` iterator.
 </span><span class="kw">pub fn </span>positions&lt;I, F&gt;(iter: I, f: F) -&gt; Positions&lt;I, F&gt;
     <span class="kw">where </span>I: Iterator,
           F: FnMut(I::Item) -&gt; bool,
 {
     Positions {
         iter,
         f,
         count: <span class="number">0
     </span>}
 }

 <span class="kw">impl</span>&lt;I, F&gt; Iterator <span class="kw">for </span>Positions&lt;I, F&gt;
     <span class="kw">where </span>I: Iterator,
           F: FnMut(I::Item) -&gt; bool,
 {
     <span class="kw">type </span>Item = usize;

     <span class="kw">fn </span>next(<span class="kw-2">&amp;mut </span><span class="self">self</span>) -&gt; <span class="prelude-ty">Option</span>&lt;<span class="self">Self</span>::Item&gt; {
         <span class="kw">while let </span><span class="prelude-val">Some</span>(v) = <span class="self">self</span>.iter.next() {
             <span class="kw">let </span>i = <span class="self">self</span>.count;
             <span class="self">self</span>.count = i + <span class="number">1</span>;
             <span class="kw">if </span>(<span class="self">self</span>.f)(v) {
                 <span class="kw">return </span><span class="prelude-val">Some</span>(i);
             }
         }
         <span class="prelude-val">None
     </span>}

     <span class="kw">fn </span>size_hint(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; (usize, <span class="prelude-ty">Option</span>&lt;usize&gt;) {
         (<span class="number">0</span>, <span class="self">self</span>.iter.size_hint().<span class="number">1</span>)
     }
 }

 <span class="kw">impl</span>&lt;I, F&gt; DoubleEndedIterator <span class="kw">for </span>Positions&lt;I, F&gt;
     <span class="kw">where </span>I: DoubleEndedIterator + ExactSizeIterator,
           F: FnMut(I::Item) -&gt; bool,
 {
     <span class="kw">fn </span>next_back(<span class="kw-2">&amp;mut </span><span class="self">self</span>) -&gt; <span class="prelude-ty">Option</span>&lt;<span class="self">Self</span>::Item&gt; {
         <span class="kw">while let </span><span class="prelude-val">Some</span>(v) = <span class="self">self</span>.iter.next_back() {
             <span class="kw">if </span>(<span class="self">self</span>.f)(v) {
                 <span class="kw">return </span><span class="prelude-val">Some</span>(<span class="self">self</span>.count + <span class="self">self</span>.iter.len())
             }
         }
         <span class="prelude-val">None
     </span>}
 }

 <span class="kw">impl</span>&lt;I, F&gt; FusedIterator <span class="kw">for </span>Positions&lt;I, F&gt;
     <span class="kw">where </span>I: FusedIterator,
           F: FnMut(I::Item) -&gt; bool,
 {}

 <span class="doccomment">/// An iterator adapter to apply a mutating function to each element before yielding it.
 ///
 /// See [`.update()`](crate::Itertools::update) for more information.
 </span><span class="attribute">#[derive(Clone)]
 #[must_use = <span class="string">&quot;iterator adaptors are lazy and do nothing unless consumed&quot;</span>]
 </span><span class="kw">pub struct </span>Update&lt;I, F&gt; {
     iter: I,
     f: F,
 }

 <span class="kw">impl</span>&lt;I, F&gt; fmt::Debug <span class="kw">for </span>Update&lt;I, F&gt;
 <span class="kw">where
     </span>I: fmt::Debug,
 {
     <span class="macro">debug_fmt_fields!</span>(Update, iter);
 }

 <span class="doccomment">/// Create a new `Update` iterator.
 </span><span class="kw">pub fn </span>update&lt;I, F&gt;(iter: I, f: F) -&gt; Update&lt;I, F&gt;
 <span class="kw">where
     </span>I: Iterator,
     F: FnMut(<span class="kw-2">&amp;mut </span>I::Item),
 {
     Update { iter, f }
 }

 <span class="kw">impl</span>&lt;I, F&gt; Iterator <span class="kw">for </span>Update&lt;I, F&gt;
 <span class="kw">where
     </span>I: Iterator,
     F: FnMut(<span class="kw-2">&amp;mut </span>I::Item),
 {
     <span class="kw">type </span>Item = I::Item;

     <span class="kw">fn </span>next(<span class="kw-2">&amp;mut </span><span class="self">self</span>) -&gt; <span class="prelude-ty">Option</span>&lt;<span class="self">Self</span>::Item&gt; {
         <span class="kw">if let </span><span class="prelude-val">Some</span>(<span class="kw-2">mut </span>v) = <span class="self">self</span>.iter.next() {
             (<span class="self">self</span>.f)(<span class="kw-2">&amp;mut </span>v);
             <span class="prelude-val">Some</span>(v)
         } <span class="kw">else </span>{
             <span class="prelude-val">None
         </span>}
     }

     <span class="kw">fn </span>size_hint(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; (usize, <span class="prelude-ty">Option</span>&lt;usize&gt;) {
         <span class="self">self</span>.iter.size_hint()
     }

     <span class="kw">fn </span>fold&lt;Acc, G&gt;(<span class="self">self</span>, init: Acc, <span class="kw-2">mut </span>g: G) -&gt; Acc
         <span class="kw">where </span>G: FnMut(Acc, <span class="self">Self</span>::Item) -&gt; Acc,
     {
         <span class="kw">let </span><span class="kw-2">mut </span>f = <span class="self">self</span>.f;
         <span class="self">self</span>.iter.fold(init, <span class="kw">move </span>|acc, <span class="kw-2">mut </span>v| { f(<span class="kw-2">&amp;mut </span>v); g(acc, v) })
     }

     <span class="comment">// if possible, re-use inner iterator specializations in collect
     </span><span class="kw">fn </span>collect&lt;C&gt;(<span class="self">self</span>) -&gt; C
         <span class="kw">where </span>C: FromIterator&lt;<span class="self">Self</span>::Item&gt;
     {
         <span class="kw">let </span><span class="kw-2">mut </span>f = <span class="self">self</span>.f;
         <span class="self">self</span>.iter.map(<span class="kw">move </span>|<span class="kw-2">mut </span>v| { f(<span class="kw-2">&amp;mut </span>v); v }).collect()
     }
 }

 <span class="kw">impl</span>&lt;I, F&gt; ExactSizeIterator <span class="kw">for </span>Update&lt;I, F&gt;
 <span class="kw">where
     </span>I: ExactSizeIterator,
     F: FnMut(<span class="kw-2">&amp;mut </span>I::Item),
 {}

 <span class="kw">impl</span>&lt;I, F&gt; DoubleEndedIterator <span class="kw">for </span>Update&lt;I, F&gt;
 <span class="kw">where
     </span>I: DoubleEndedIterator,
     F: FnMut(<span class="kw-2">&amp;mut </span>I::Item),
 {
     <span class="kw">fn </span>next_back(<span class="kw-2">&amp;mut </span><span class="self">self</span>) -&gt; <span class="prelude-ty">Option</span>&lt;<span class="self">Self</span>::Item&gt; {
         <span class="kw">if let </span><span class="prelude-val">Some</span>(<span class="kw-2">mut </span>v) = <span class="self">self</span>.iter.next_back() {
             (<span class="self">self</span>.f)(<span class="kw-2">&amp;mut </span>v);
             <span class="prelude-val">Some</span>(v)
         } <span class="kw">else </span>{
             <span class="prelude-val">None
         </span>}
     }
 }

 <span class="kw">impl</span>&lt;I, F&gt; FusedIterator <span class="kw">for </span>Update&lt;I, F&gt;
 <span class="kw">where
     </span>I: FusedIterator,
     F: FnMut(<span class="kw-2">&amp;mut </span>I::Item),
 {}
 </code></pre></div>
 </section></div></main><div id="rustdoc-vars" data-root-path="../../../" data-current-crate="itertools" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html>