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<span class="kw">use</span> <span class="ident">std::iter::Peekable</span>;
<span class="kw">use</span> <span class="ident">PutBack</span>;
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"use_std"</span>)]</span>
<span class="kw">use</span> <span class="ident">PutBackN</span>;
<span class="doccomment">/// An iterator that allows peeking at an element before deciding to accept it.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// See [`.peeking_take_while()`](trait.Itertools.html#method.peeking_take_while)</span>
<span class="doccomment">/// for more information.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This is implemented by peeking adaptors like peekable and put back,</span>
<span class="doccomment">/// but also by a few iterators that can be peeked natively, like the slice’s</span>
<span class="doccomment">/// by reference iterator (`std::slice::Iter`).</span>
<span class="kw">pub</span> <span class="kw">trait</span> <span class="ident">PeekingNext</span> : <span class="ident">Iterator</span> {
<span class="doccomment">/// Pass a reference to the next iterator element to the closure `accept`;</span>
<span class="doccomment">/// if `accept` returns true, return it as the next element,</span>
<span class="doccomment">/// else None.</span>
<span class="kw">fn</span> <span class="ident">peeking_next</span><span class="op"><</span><span class="ident">F</span><span class="op">></span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">accept</span>: <span class="ident">F</span>) <span class="op">-</span><span class="op">></span> <span class="prelude-ty">Option</span><span class="op"><</span><span class="self">Self</span><span class="ident">::Item</span><span class="op">></span>
<span class="kw">where</span> <span class="ident">F</span>: <span class="ident">FnOnce</span>(<span class="kw-2">&</span><span class="self">Self</span><span class="ident">::Item</span>) <span class="op">-</span><span class="op">></span> <span class="ident">bool</span>;
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">I</span><span class="op">></span> <span class="ident">PeekingNext</span> <span class="kw">for</span> <span class="ident">Peekable</span><span class="op"><</span><span class="ident">I</span><span class="op">></span>
<span class="kw">where</span> <span class="ident">I</span>: <span class="ident">Iterator</span>,
{
<span class="kw">fn</span> <span class="ident">peeking_next</span><span class="op"><</span><span class="ident">F</span><span class="op">></span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">accept</span>: <span class="ident">F</span>) <span class="op">-</span><span class="op">></span> <span class="prelude-ty">Option</span><span class="op"><</span><span class="self">Self</span><span class="ident">::Item</span><span class="op">></span>
<span class="kw">where</span> <span class="ident">F</span>: <span class="ident">FnOnce</span>(<span class="kw-2">&</span><span class="self">Self</span><span class="ident">::Item</span>) <span class="op">-</span><span class="op">></span> <span class="ident">bool</span>
{
<span class="kw">if</span> <span class="kw">let</span> <span class="prelude-val">Some</span>(<span class="ident">r</span>) <span class="op">=</span> <span class="self">self</span>.<span class="ident">peek</span>() {
<span class="kw">if</span> <span class="op">!</span><span class="ident">accept</span>(<span class="ident">r</span>) {
<span class="kw">return</span> <span class="prelude-val">None</span>;
}
}
<span class="self">self</span>.<span class="ident">next</span>()
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">I</span><span class="op">></span> <span class="ident">PeekingNext</span> <span class="kw">for</span> <span class="ident">PutBack</span><span class="op"><</span><span class="ident">I</span><span class="op">></span>
<span class="kw">where</span> <span class="ident">I</span>: <span class="ident">Iterator</span>,
{
<span class="kw">fn</span> <span class="ident">peeking_next</span><span class="op"><</span><span class="ident">F</span><span class="op">></span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">accept</span>: <span class="ident">F</span>) <span class="op">-</span><span class="op">></span> <span class="prelude-ty">Option</span><span class="op"><</span><span class="self">Self</span><span class="ident">::Item</span><span class="op">></span>
<span class="kw">where</span> <span class="ident">F</span>: <span class="ident">FnOnce</span>(<span class="kw-2">&</span><span class="self">Self</span><span class="ident">::Item</span>) <span class="op">-</span><span class="op">></span> <span class="ident">bool</span>
{
<span class="kw">if</span> <span class="kw">let</span> <span class="prelude-val">Some</span>(<span class="ident">r</span>) <span class="op">=</span> <span class="self">self</span>.<span class="ident">next</span>() {
<span class="kw">if</span> <span class="op">!</span><span class="ident">accept</span>(<span class="kw-2">&</span><span class="ident">r</span>) {
<span class="self">self</span>.<span class="ident">put_back</span>(<span class="ident">r</span>);
<span class="kw">return</span> <span class="prelude-val">None</span>;
}
<span class="prelude-val">Some</span>(<span class="ident">r</span>)
} <span class="kw">else</span> {
<span class="prelude-val">None</span>
}
}
}
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"use_std"</span>)]</span>
<span class="kw">impl</span><span class="op"><</span><span class="ident">I</span><span class="op">></span> <span class="ident">PeekingNext</span> <span class="kw">for</span> <span class="ident">PutBackN</span><span class="op"><</span><span class="ident">I</span><span class="op">></span>
<span class="kw">where</span> <span class="ident">I</span>: <span class="ident">Iterator</span>,
{
<span class="kw">fn</span> <span class="ident">peeking_next</span><span class="op"><</span><span class="ident">F</span><span class="op">></span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">accept</span>: <span class="ident">F</span>) <span class="op">-</span><span class="op">></span> <span class="prelude-ty">Option</span><span class="op"><</span><span class="self">Self</span><span class="ident">::Item</span><span class="op">></span>
<span class="kw">where</span> <span class="ident">F</span>: <span class="ident">FnOnce</span>(<span class="kw-2">&</span><span class="self">Self</span><span class="ident">::Item</span>) <span class="op">-</span><span class="op">></span> <span class="ident">bool</span>
{
<span class="kw">if</span> <span class="kw">let</span> <span class="prelude-val">Some</span>(<span class="ident">r</span>) <span class="op">=</span> <span class="self">self</span>.<span class="ident">next</span>() {
<span class="kw">if</span> <span class="op">!</span><span class="ident">accept</span>(<span class="kw-2">&</span><span class="ident">r</span>) {
<span class="self">self</span>.<span class="ident">put_back</span>(<span class="ident">r</span>);
<span class="kw">return</span> <span class="prelude-val">None</span>;
}
<span class="prelude-val">Some</span>(<span class="ident">r</span>)
} <span class="kw">else</span> {
<span class="prelude-val">None</span>
}
}
}
<span class="doccomment">/// An iterator adaptor that takes items while a closure returns `true`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// See [`.peeking_take_while()`](../trait.Itertools.html#method.peeking_take_while)</span>
<span class="doccomment">/// for more information.</span>
<span class="attribute">#[<span class="ident">must_use</span> <span class="op">=</span> <span class="string">"iterator adaptors are lazy and do nothing unless consumed"</span>]</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">PeekingTakeWhile</span><span class="op"><</span><span class="lifetime">'a</span>, <span class="ident">I</span>: <span class="lifetime">'a</span>, <span class="ident">F</span><span class="op">></span>
<span class="kw">where</span> <span class="ident">I</span>: <span class="ident">Iterator</span>,
{
<span class="ident">iter</span>: <span class="kw-2">&</span><span class="lifetime">'a</span> <span class="kw-2">mut</span> <span class="ident">I</span>,
<span class="ident">f</span>: <span class="ident">F</span>,
}
<span class="doccomment">/// Create a PeekingTakeWhile</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">peeking_take_while</span><span class="op"><</span><span class="ident">I</span>, <span class="ident">F</span><span class="op">></span>(<span class="ident">iter</span>: <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">I</span>, <span class="ident">f</span>: <span class="ident">F</span>) <span class="op">-</span><span class="op">></span> <span class="ident">PeekingTakeWhile</span><span class="op"><</span><span class="ident">I</span>, <span class="ident">F</span><span class="op">></span>
<span class="kw">where</span> <span class="ident">I</span>: <span class="ident">Iterator</span>,
{
<span class="ident">PeekingTakeWhile</span> {
<span class="ident">iter</span>: <span class="ident">iter</span>,
<span class="ident">f</span>: <span class="ident">f</span>,
}
}
<span class="kw">impl</span><span class="op"><</span><span class="lifetime">'a</span>, <span class="ident">I</span>, <span class="ident">F</span><span class="op">></span> <span class="ident">Iterator</span> <span class="kw">for</span> <span class="ident">PeekingTakeWhile</span><span class="op"><</span><span class="lifetime">'a</span>, <span class="ident">I</span>, <span class="ident">F</span><span class="op">></span>
<span class="kw">where</span> <span class="ident">I</span>: <span class="ident">PeekingNext</span>,
<span class="ident">F</span>: <span class="ident">FnMut</span>(<span class="kw-2">&</span><span class="ident">I::Item</span>) <span class="op">-</span><span class="op">></span> <span class="ident">bool</span>,
{
<span class="kw">type</span> <span class="ident">Item</span> <span class="op">=</span> <span class="ident">I::Item</span>;
<span class="kw">fn</span> <span class="ident">next</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-</span><span class="op">></span> <span class="prelude-ty">Option</span><span class="op"><</span><span class="self">Self</span><span class="ident">::Item</span><span class="op">></span> {
<span class="self">self</span>.<span class="ident">iter</span>.<span class="ident">peeking_next</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>.<span class="ident">f</span>)
}
<span class="kw">fn</span> <span class="ident">size_hint</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-</span><span class="op">></span> (<span class="ident">usize</span>, <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">usize</span><span class="op">></span>) {
<span class="kw">let</span> (<span class="kw">_</span>, <span class="ident">hi</span>) <span class="op">=</span> <span class="self">self</span>.<span class="ident">iter</span>.<span class="ident">size_hint</span>();
(<span class="number">0</span>, <span class="ident">hi</span>)
}
}
<span class="comment">// Some iterators are so lightweight we can simply clone them to save their</span>
<span class="comment">// state and use that for peeking.</span>
<span class="macro">macro_rules!</span> <span class="ident">peeking_next_by_clone</span> {
([$(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">typarm</span>:<span class="ident">tt</span>)<span class="kw-2">*</span>] <span class="macro-nonterminal">$</span><span class="macro-nonterminal">type_</span>:<span class="ident">ty</span>) <span class="op">=</span><span class="op">></span> {
<span class="kw">impl</span><span class="op"><</span>$(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">typarm</span>)<span class="kw-2">*</span><span class="op">></span> <span class="ident">PeekingNext</span> <span class="kw">for</span> <span class="macro-nonterminal">$</span><span class="macro-nonterminal">type_</span> {
<span class="kw">fn</span> <span class="ident">peeking_next</span><span class="op"><</span><span class="ident">F</span><span class="op">></span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">accept</span>: <span class="ident">F</span>) <span class="op">-</span><span class="op">></span> <span class="prelude-ty">Option</span><span class="op"><</span><span class="self">Self</span><span class="ident">::Item</span><span class="op">></span>
<span class="kw">where</span> <span class="ident">F</span>: <span class="ident">FnOnce</span>(<span class="kw-2">&</span><span class="self">Self</span><span class="ident">::Item</span>) <span class="op">-</span><span class="op">></span> <span class="ident">bool</span>
{
<span class="kw">let</span> <span class="ident">saved_state</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">clone</span>();
<span class="kw">if</span> <span class="kw">let</span> <span class="prelude-val">Some</span>(<span class="ident">r</span>) <span class="op">=</span> <span class="self">self</span>.<span class="ident">next</span>() {
<span class="kw">if</span> <span class="op">!</span><span class="ident">accept</span>(<span class="kw-2">&</span><span class="ident">r</span>) {
<span class="kw-2">*</span><span class="self">self</span> <span class="op">=</span> <span class="ident">saved_state</span>;
} <span class="kw">else</span> {
<span class="kw">return</span> <span class="prelude-val">Some</span>(<span class="ident">r</span>)
}
}
<span class="prelude-val">None</span>
}
}
}
}
<span class="macro">peeking_next_by_clone!</span> { [<span class="lifetime">'a</span>, <span class="ident">T</span>] <span class="ident">::std::slice::Iter</span><span class="op"><</span><span class="lifetime">'a</span>, <span class="ident">T</span><span class="op">></span> }
<span class="macro">peeking_next_by_clone!</span> { [<span class="lifetime">'a</span>] <span class="ident">::std::str::Chars</span><span class="op"><</span><span class="lifetime">'a</span><span class="op">></span> }
<span class="macro">peeking_next_by_clone!</span> { [<span class="lifetime">'a</span>] <span class="ident">::std::str::CharIndices</span><span class="op"><</span><span class="lifetime">'a</span><span class="op">></span> }
<span class="macro">peeking_next_by_clone!</span> { [<span class="lifetime">'a</span>] <span class="ident">::std::str::Bytes</span><span class="op"><</span><span class="lifetime">'a</span><span class="op">></span> }
<span class="macro">peeking_next_by_clone!</span> { [<span class="lifetime">'a</span>, <span class="ident">T</span>] <span class="ident">::std::option::Iter</span><span class="op"><</span><span class="lifetime">'a</span>, <span class="ident">T</span><span class="op">></span> }
<span class="macro">peeking_next_by_clone!</span> { [<span class="lifetime">'a</span>, <span class="ident">T</span>] <span class="ident">::std::result::Iter</span><span class="op"><</span><span class="lifetime">'a</span>, <span class="ident">T</span><span class="op">></span> }
<span class="macro">peeking_next_by_clone!</span> { [<span class="ident">T</span>] <span class="ident">::std::iter::Empty</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> }
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"use_std"</span>)]</span>
<span class="macro">peeking_next_by_clone!</span> { [<span class="lifetime">'a</span>, <span class="ident">T</span>] <span class="ident">::std::collections::linked_list::Iter</span><span class="op"><</span><span class="lifetime">'a</span>, <span class="ident">T</span><span class="op">></span> }
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"use_std"</span>)]</span>
<span class="macro">peeking_next_by_clone!</span> { [<span class="lifetime">'a</span>, <span class="ident">T</span>] <span class="ident">::std::collections::vec_deque::Iter</span><span class="op"><</span><span class="lifetime">'a</span>, <span class="ident">T</span><span class="op">></span> }
<span class="comment">// cloning a Rev has no extra overhead; peekable and put backs are never DEI.</span>
<span class="macro">peeking_next_by_clone!</span> { [<span class="ident">I</span>: <span class="ident">Clone</span> <span class="op">+</span> <span class="ident">PeekingNext</span> <span class="op">+</span> <span class="ident">DoubleEndedIterator</span>]
<span class="ident">::std::iter::Rev</span><span class="op"><</span><span class="ident">I</span><span class="op">></span> }
</pre></div>
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