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</pre><pre class="rust ">
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">cmp</span>::<span class="ident">Ordering</span>::{<span class="ident">Equal</span>, <span class="ident">Greater</span>, <span class="ident">Less</span>};
<span class="kw">use</span> <span class="kw">super</span>::<span class="ident">size_hint</span>;
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">iter</span>::<span class="ident">Fuse</span>;
<span class="kw">use</span> <span class="self">self</span>::<span class="ident">EitherOrBoth</span>::{<span class="ident">Right</span>, <span class="ident">Left</span>, <span class="ident">Both</span>};
<span class="comment">// ZipLongest originally written by SimonSapin,</span>
<span class="comment">// and dedicated to itertools https://github.com/rust-lang/rust/pull/19283</span>
<span class="doccomment">/// An iterator which iterates two other iterators simultaneously</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This iterator is *fused*.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// See [`.zip_longest()`](../trait.Itertools.html#method.zip_longest) for more information.</span>
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Clone</span>)]</span>
<span class="attribute">#[<span class="ident">must_use</span> <span class="op">=</span> <span class="string">&quot;iterator adaptors are lazy and do nothing unless consumed&quot;</span>]</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">ZipLongest</span><span class="op">&lt;</span><span class="ident">T</span>, <span class="ident">U</span><span class="op">&gt;</span> {
<span class="ident">a</span>: <span class="ident">Fuse</span><span class="op">&lt;</span><span class="ident">T</span><span class="op">&gt;</span>,
<span class="ident">b</span>: <span class="ident">Fuse</span><span class="op">&lt;</span><span class="ident">U</span><span class="op">&gt;</span>,
}
<span class="doccomment">/// Create a new `ZipLongest` iterator.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">zip_longest</span><span class="op">&lt;</span><span class="ident">T</span>, <span class="ident">U</span><span class="op">&gt;</span>(<span class="ident">a</span>: <span class="ident">T</span>, <span class="ident">b</span>: <span class="ident">U</span>) <span class="op">-&gt;</span> <span class="ident">ZipLongest</span><span class="op">&lt;</span><span class="ident">T</span>, <span class="ident">U</span><span class="op">&gt;</span>
<span class="kw">where</span> <span class="ident">T</span>: <span class="ident">Iterator</span>,
<span class="ident">U</span>: <span class="ident">Iterator</span>
{
<span class="ident">ZipLongest</span> {
<span class="ident">a</span>: <span class="ident">a</span>.<span class="ident">fuse</span>(),
<span class="ident">b</span>: <span class="ident">b</span>.<span class="ident">fuse</span>(),
}
}
<span class="kw">impl</span><span class="op">&lt;</span><span class="ident">T</span>, <span class="ident">U</span><span class="op">&gt;</span> <span class="ident">Iterator</span> <span class="kw">for</span> <span class="ident">ZipLongest</span><span class="op">&lt;</span><span class="ident">T</span>, <span class="ident">U</span><span class="op">&gt;</span>
<span class="kw">where</span> <span class="ident">T</span>: <span class="ident">Iterator</span>,
<span class="ident">U</span>: <span class="ident">Iterator</span>
{
<span class="kw">type</span> <span class="ident">Item</span> <span class="op">=</span> <span class="ident">EitherOrBoth</span><span class="op">&lt;</span><span class="ident">T</span>::<span class="ident">Item</span>, <span class="ident">U</span>::<span class="ident">Item</span><span class="op">&gt;</span>;
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">fn</span> <span class="ident">next</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-&gt;</span> <span class="prelude-ty">Option</span><span class="op">&lt;</span><span class="self">Self</span>::<span class="ident">Item</span><span class="op">&gt;</span> {
<span class="kw">match</span> (<span class="self">self</span>.<span class="ident">a</span>.<span class="ident">next</span>(), <span class="self">self</span>.<span class="ident">b</span>.<span class="ident">next</span>()) {
(<span class="prelude-val">None</span>, <span class="prelude-val">None</span>) <span class="op">=&gt;</span> <span class="prelude-val">None</span>,
(<span class="prelude-val">Some</span>(<span class="ident">a</span>), <span class="prelude-val">None</span>) <span class="op">=&gt;</span> <span class="prelude-val">Some</span>(<span class="ident">Left</span>(<span class="ident">a</span>)),
(<span class="prelude-val">None</span>, <span class="prelude-val">Some</span>(<span class="ident">b</span>)) <span class="op">=&gt;</span> <span class="prelude-val">Some</span>(<span class="ident">Right</span>(<span class="ident">b</span>)),
(<span class="prelude-val">Some</span>(<span class="ident">a</span>), <span class="prelude-val">Some</span>(<span class="ident">b</span>)) <span class="op">=&gt;</span> <span class="prelude-val">Some</span>(<span class="ident">Both</span>(<span class="ident">a</span>, <span class="ident">b</span>)),
}
}
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">fn</span> <span class="ident">size_hint</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-&gt;</span> (<span class="ident">usize</span>, <span class="prelude-ty">Option</span><span class="op">&lt;</span><span class="ident">usize</span><span class="op">&gt;</span>) {
<span class="ident">size_hint</span>::<span class="ident">max</span>(<span class="self">self</span>.<span class="ident">a</span>.<span class="ident">size_hint</span>(), <span class="self">self</span>.<span class="ident">b</span>.<span class="ident">size_hint</span>())
}
}
<span class="kw">impl</span><span class="op">&lt;</span><span class="ident">T</span>, <span class="ident">U</span><span class="op">&gt;</span> <span class="ident">DoubleEndedIterator</span> <span class="kw">for</span> <span class="ident">ZipLongest</span><span class="op">&lt;</span><span class="ident">T</span>, <span class="ident">U</span><span class="op">&gt;</span>
<span class="kw">where</span> <span class="ident">T</span>: <span class="ident">DoubleEndedIterator</span> <span class="op">+</span> <span class="ident">ExactSizeIterator</span>,
<span class="ident">U</span>: <span class="ident">DoubleEndedIterator</span> <span class="op">+</span> <span class="ident">ExactSizeIterator</span>
{
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">fn</span> <span class="ident">next_back</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-&gt;</span> <span class="prelude-ty">Option</span><span class="op">&lt;</span><span class="self">Self</span>::<span class="ident">Item</span><span class="op">&gt;</span> {
<span class="kw">match</span> <span class="self">self</span>.<span class="ident">a</span>.<span class="ident">len</span>().<span class="ident">cmp</span>(<span class="kw-2">&amp;</span><span class="self">self</span>.<span class="ident">b</span>.<span class="ident">len</span>()) {
<span class="ident">Equal</span> <span class="op">=&gt;</span> <span class="kw">match</span> (<span class="self">self</span>.<span class="ident">a</span>.<span class="ident">next_back</span>(), <span class="self">self</span>.<span class="ident">b</span>.<span class="ident">next_back</span>()) {
(<span class="prelude-val">None</span>, <span class="prelude-val">None</span>) <span class="op">=&gt;</span> <span class="prelude-val">None</span>,
(<span class="prelude-val">Some</span>(<span class="ident">a</span>), <span class="prelude-val">Some</span>(<span class="ident">b</span>)) <span class="op">=&gt;</span> <span class="prelude-val">Some</span>(<span class="ident">Both</span>(<span class="ident">a</span>, <span class="ident">b</span>)),
<span class="comment">// These can only happen if .len() is inconsistent with .next_back()</span>
(<span class="prelude-val">Some</span>(<span class="ident">a</span>), <span class="prelude-val">None</span>) <span class="op">=&gt;</span> <span class="prelude-val">Some</span>(<span class="ident">Left</span>(<span class="ident">a</span>)),
(<span class="prelude-val">None</span>, <span class="prelude-val">Some</span>(<span class="ident">b</span>)) <span class="op">=&gt;</span> <span class="prelude-val">Some</span>(<span class="ident">Right</span>(<span class="ident">b</span>)),
},
<span class="ident">Greater</span> <span class="op">=&gt;</span> <span class="self">self</span>.<span class="ident">a</span>.<span class="ident">next_back</span>().<span class="ident">map</span>(<span class="ident">Left</span>),
<span class="ident">Less</span> <span class="op">=&gt;</span> <span class="self">self</span>.<span class="ident">b</span>.<span class="ident">next_back</span>().<span class="ident">map</span>(<span class="ident">Right</span>),
}
}
}
<span class="kw">impl</span><span class="op">&lt;</span><span class="ident">T</span>, <span class="ident">U</span><span class="op">&gt;</span> <span class="ident">ExactSizeIterator</span> <span class="kw">for</span> <span class="ident">ZipLongest</span><span class="op">&lt;</span><span class="ident">T</span>, <span class="ident">U</span><span class="op">&gt;</span>
<span class="kw">where</span> <span class="ident">T</span>: <span class="ident">ExactSizeIterator</span>,
<span class="ident">U</span>: <span class="ident">ExactSizeIterator</span>
{}
<span class="doccomment">/// A value yielded by `ZipLongest`.</span>
<span class="doccomment">/// Contains one or two values, depending on which of the input iterators are exhausted.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// See [`.zip_longest()`](trait.Itertools.html#method.zip_longest) for more information.</span>
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Clone</span>, <span class="ident">PartialEq</span>, <span class="ident">Eq</span>, <span class="ident">Debug</span>)]</span>
<span class="kw">pub</span> <span class="kw">enum</span> <span class="ident">EitherOrBoth</span><span class="op">&lt;</span><span class="ident">A</span>, <span class="ident">B</span><span class="op">&gt;</span> {
<span class="doccomment">/// Neither input iterator is exhausted yet, yielding two values.</span>
<span class="ident">Both</span>(<span class="ident">A</span>, <span class="ident">B</span>),
<span class="doccomment">/// The parameter iterator of `.zip_longest()` is exhausted,</span>
<span class="doccomment">/// only yielding a value from the `self` iterator.</span>
<span class="ident">Left</span>(<span class="ident">A</span>),
<span class="doccomment">/// The `self` iterator of `.zip_longest()` is exhausted,</span>
<span class="doccomment">/// only yielding a value from the parameter iterator.</span>
<span class="ident">Right</span>(<span class="ident">B</span>),
}
</pre>
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