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class="content"><div class="main-heading"><h1 class="fqn">Function <a href="index.html">itertools</a>::<wbr><a class="fn" href="#">unfold</a><button id="copy-path" onclick="copy_path(this)" title="Copy item path to clipboard"><img src="../clipboard.svg" width="19" height="18" alt="Copy item path"></button></h1><span class="out-of-band"><a class="srclink" href="../src/itertools/sources.rs.html#100-107">source</a> · <a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">[<span class="inner">−</span>]</a></span></div><div class="item-decl"><pre class="rust fn"><code>pub fn unfold<A, St, F>(initial_state: St, f: F) -> <a class="struct" href="structs/struct.Unfold.html" title="struct itertools::structs::Unfold">Unfold</a><St, F><span class="notable-traits"><span class="notable-traits-tooltip">ⓘ<span class="notable-traits-tooltiptext"><span class="docblock"><span class="notable">Notable traits for <a class="struct" href="structs/struct.Unfold.html" title="struct itertools::structs::Unfold">Unfold</a><St, F></span><code class="content"><span class="where fmt-newline">impl<A, St, F> <a class="trait" href="https://doc.rust-lang.org/nightly/core/iter/traits/iterator/trait.Iterator.html" title="trait core::iter::traits::iterator::Iterator">Iterator</a> for <a class="struct" href="structs/struct.Unfold.html" title="struct itertools::structs::Unfold">Unfold</a><St, F><span class="where fmt-newline">where<br> F: <a class="trait" href="https://doc.rust-lang.org/nightly/core/ops/function/trait.FnMut.html" title="trait core::ops::function::FnMut">FnMut</a>(<a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.reference.html">&mut </a>St) -> <a class="enum" href="https://doc.rust-lang.org/nightly/core/option/enum.Option.html" title="enum core::option::Option">Option</a><A>,</span></span><span class="where fmt-newline"> type <a href="https://doc.rust-lang.org/nightly/core/iter/traits/iterator/trait.Iterator.html#associatedtype.Item" class="associatedtype">Item</a> = A;</span></code></span></span></span></span><span class="where fmt-newline">where<br> F: <a class="trait" href="https://doc.rust-lang.org/nightly/core/ops/function/trait.FnMut.html" title="trait core::ops::function::FnMut">FnMut</a>(<a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.reference.html">&mut </a>St) -> <a class="enum" href="https://doc.rust-lang.org/nightly/core/option/enum.Option.html" title="enum core::option::Option">Option</a><A>,</span></code></pre></div><details class="rustdoc-toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Creates a new unfold source with the specified closure as the “iterator |
| function” and an initial state to eventually pass to the closure</p> |
| <p><code>unfold</code> is a general iterator builder: it has a mutable state value, |
| and a closure with access to the state that produces the next value.</p> |
| <p>This more or less equivalent to a regular struct with an <code>Iterator</code> |
| implementation, and is useful for one-off iterators.</p> |
| |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="comment">// an iterator that yields sequential Fibonacci numbers, |
| // and stops at the maximum representable value. |
| |
| </span><span class="kw">use </span>itertools::unfold; |
| |
| <span class="kw">let </span>(<span class="kw-2">mut </span>x1, <span class="kw-2">mut </span>x2) = (<span class="number">1u32</span>, <span class="number">1u32</span>); |
| <span class="kw">let </span><span class="kw-2">mut </span>fibonacci = unfold((), <span class="kw">move </span>|<span class="kw">_</span>| { |
| <span class="comment">// Attempt to get the next Fibonacci number |
| </span><span class="kw">let </span>next = x1.saturating_add(x2); |
| |
| <span class="comment">// Shift left: ret <- x1 <- x2 <- next |
| </span><span class="kw">let </span>ret = x1; |
| x1 = x2; |
| x2 = next; |
| |
| <span class="comment">// If addition has saturated at the maximum, we are finished |
| </span><span class="kw">if </span>ret == x1 && ret > <span class="number">1 </span>{ |
| <span class="kw">return </span><span class="prelude-val">None</span>; |
| } |
| |
| <span class="prelude-val">Some</span>(ret) |
| }); |
| |
| itertools::assert_equal(fibonacci.by_ref().take(<span class="number">8</span>), |
| <span class="macro">vec!</span>[<span class="number">1</span>, <span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span>, <span class="number">5</span>, <span class="number">8</span>, <span class="number">13</span>, <span class="number">21</span>]); |
| <span class="macro">assert_eq!</span>(fibonacci.last(), <span class="prelude-val">Some</span>(<span class="number">2_971_215_073</span>))</code></pre></div> |
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