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| </pre><pre class="rust"><code><span class="kw">use </span>std::iter::Peekable; |
| <span class="kw">use </span><span class="kw">crate</span>::PutBack; |
| <span class="attribute">#[cfg(feature = <span class="string">"use_alloc"</span>)] |
| </span><span class="kw">use </span><span class="kw">crate</span>::PutBackN; |
| |
| <span class="doccomment">/// An iterator that allows peeking at an element before deciding to accept it. |
| /// |
| /// See [`.peeking_take_while()`](crate::Itertools::peeking_take_while) |
| /// for more information. |
| /// |
| /// This is implemented by peeking adaptors like peekable and put back, |
| /// but also by a few iterators that can be peeked natively, like the slice’s |
| /// by reference iterator (`std::slice::Iter`). |
| </span><span class="kw">pub trait </span>PeekingNext : Iterator { |
| <span class="doccomment">/// Pass a reference to the next iterator element to the closure `accept`; |
| /// if `accept` returns true, return it as the next element, |
| /// else None. |
| </span><span class="kw">fn </span>peeking_next<F>(<span class="kw-2">&mut </span><span class="self">self</span>, accept: F) -> <span class="prelude-ty">Option</span><<span class="self">Self</span>::Item> |
| <span class="kw">where </span>F: FnOnce(<span class="kw-2">&</span><span class="self">Self</span>::Item) -> bool; |
| } |
| |
| <span class="kw">impl</span><I> PeekingNext <span class="kw">for </span>Peekable<I> |
| <span class="kw">where </span>I: Iterator, |
| { |
| <span class="kw">fn </span>peeking_next<F>(<span class="kw-2">&mut </span><span class="self">self</span>, accept: F) -> <span class="prelude-ty">Option</span><<span class="self">Self</span>::Item> |
| <span class="kw">where </span>F: FnOnce(<span class="kw-2">&</span><span class="self">Self</span>::Item) -> bool |
| { |
| <span class="kw">if let </span><span class="prelude-val">Some</span>(r) = <span class="self">self</span>.peek() { |
| <span class="kw">if </span>!accept(r) { |
| <span class="kw">return </span><span class="prelude-val">None</span>; |
| } |
| } |
| <span class="self">self</span>.next() |
| } |
| } |
| |
| <span class="kw">impl</span><I> PeekingNext <span class="kw">for </span>PutBack<I> |
| <span class="kw">where </span>I: Iterator, |
| { |
| <span class="kw">fn </span>peeking_next<F>(<span class="kw-2">&mut </span><span class="self">self</span>, accept: F) -> <span class="prelude-ty">Option</span><<span class="self">Self</span>::Item> |
| <span class="kw">where </span>F: FnOnce(<span class="kw-2">&</span><span class="self">Self</span>::Item) -> bool |
| { |
| <span class="kw">if let </span><span class="prelude-val">Some</span>(r) = <span class="self">self</span>.next() { |
| <span class="kw">if </span>!accept(<span class="kw-2">&</span>r) { |
| <span class="self">self</span>.put_back(r); |
| <span class="kw">return </span><span class="prelude-val">None</span>; |
| } |
| <span class="prelude-val">Some</span>(r) |
| } <span class="kw">else </span>{ |
| <span class="prelude-val">None |
| </span>} |
| } |
| } |
| |
| <span class="attribute">#[cfg(feature = <span class="string">"use_alloc"</span>)] |
| </span><span class="kw">impl</span><I> PeekingNext <span class="kw">for </span>PutBackN<I> |
| <span class="kw">where </span>I: Iterator, |
| { |
| <span class="kw">fn </span>peeking_next<F>(<span class="kw-2">&mut </span><span class="self">self</span>, accept: F) -> <span class="prelude-ty">Option</span><<span class="self">Self</span>::Item> |
| <span class="kw">where </span>F: FnOnce(<span class="kw-2">&</span><span class="self">Self</span>::Item) -> bool |
| { |
| <span class="kw">if let </span><span class="prelude-val">Some</span>(r) = <span class="self">self</span>.next() { |
| <span class="kw">if </span>!accept(<span class="kw-2">&</span>r) { |
| <span class="self">self</span>.put_back(r); |
| <span class="kw">return </span><span class="prelude-val">None</span>; |
| } |
| <span class="prelude-val">Some</span>(r) |
| } <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`. |
| /// |
| /// See [`.peeking_take_while()`](crate::Itertools::peeking_take_while) |
| /// for more information. |
| </span><span class="attribute">#[must_use = <span class="string">"iterator adaptors are lazy and do nothing unless consumed"</span>] |
| </span><span class="kw">pub struct </span>PeekingTakeWhile<<span class="lifetime">'a</span>, I: <span class="lifetime">'a</span>, F> |
| <span class="kw">where </span>I: Iterator, |
| { |
| iter: <span class="kw-2">&</span><span class="lifetime">'a </span><span class="kw-2">mut </span>I, |
| f: F, |
| } |
| |
| <span class="kw">impl</span><<span class="lifetime">'a</span>, I: <span class="lifetime">'a</span>, F> std::fmt::Debug <span class="kw">for </span>PeekingTakeWhile<<span class="lifetime">'a</span>, I, F> |
| <span class="kw">where |
| </span>I: Iterator + std::fmt::Debug, |
| { |
| <span class="macro">debug_fmt_fields!</span>(PeekingTakeWhile, iter); |
| } |
| |
| <span class="doccomment">/// Create a `PeekingTakeWhile` |
| </span><span class="kw">pub fn </span>peeking_take_while<I, F>(iter: <span class="kw-2">&mut </span>I, f: F) -> PeekingTakeWhile<I, F> |
| <span class="kw">where </span>I: Iterator, |
| { |
| PeekingTakeWhile { |
| iter, |
| f, |
| } |
| } |
| |
| <span class="kw">impl</span><<span class="lifetime">'a</span>, I, F> Iterator <span class="kw">for </span>PeekingTakeWhile<<span class="lifetime">'a</span>, I, F> |
| <span class="kw">where </span>I: PeekingNext, |
| F: FnMut(<span class="kw-2">&</span>I::Item) -> bool, |
| |
| { |
| <span class="kw">type </span>Item = I::Item; |
| <span class="kw">fn </span>next(<span class="kw-2">&mut </span><span class="self">self</span>) -> <span class="prelude-ty">Option</span><<span class="self">Self</span>::Item> { |
| <span class="self">self</span>.iter.peeking_next(<span class="kw-2">&mut </span><span class="self">self</span>.f) |
| } |
| |
| <span class="kw">fn </span>size_hint(<span class="kw-2">&</span><span class="self">self</span>) -> (usize, <span class="prelude-ty">Option</span><usize>) { |
| (<span class="number">0</span>, <span class="self">self</span>.iter.size_hint().<span class="number">1</span>) |
| } |
| } |
| |
| <span class="comment">// Some iterators are so lightweight we can simply clone them to save their |
| // state and use that for peeking. |
| </span><span class="macro">macro_rules! </span>peeking_next_by_clone { |
| ([$(<span class="macro-nonterminal">$typarm</span>:tt)<span class="kw-2">*</span>] <span class="macro-nonterminal">$type_</span>:ty) => { |
| <span class="kw">impl</span><$(<span class="macro-nonterminal">$typarm</span>)<span class="kw-2">*</span>> PeekingNext <span class="kw">for </span><span class="macro-nonterminal">$type_ </span>{ |
| <span class="kw">fn </span>peeking_next<F>(<span class="kw-2">&mut </span><span class="self">self</span>, accept: F) -> <span class="prelude-ty">Option</span><<span class="self">Self</span>::Item> |
| <span class="kw">where </span>F: FnOnce(<span class="kw-2">&</span><span class="self">Self</span>::Item) -> bool |
| { |
| <span class="kw">let </span>saved_state = <span class="self">self</span>.clone(); |
| <span class="kw">if let </span><span class="prelude-val">Some</span>(r) = <span class="self">self</span>.next() { |
| <span class="kw">if </span>!accept(<span class="kw-2">&</span>r) { |
| <span class="kw-2">*</span><span class="self">self </span>= saved_state; |
| } <span class="kw">else </span>{ |
| <span class="kw">return </span><span class="prelude-val">Some</span>(r) |
| } |
| } |
| <span class="prelude-val">None |
| </span>} |
| } |
| } |
| } |
| |
| <span class="macro">peeking_next_by_clone! </span>{ [<span class="lifetime">'a</span>, T] ::std::slice::Iter<<span class="lifetime">'a</span>, T> } |
| <span class="macro">peeking_next_by_clone! </span>{ [<span class="lifetime">'a</span>] ::std::str::Chars<<span class="lifetime">'a</span>> } |
| <span class="macro">peeking_next_by_clone! </span>{ [<span class="lifetime">'a</span>] ::std::str::CharIndices<<span class="lifetime">'a</span>> } |
| <span class="macro">peeking_next_by_clone! </span>{ [<span class="lifetime">'a</span>] ::std::str::Bytes<<span class="lifetime">'a</span>> } |
| <span class="macro">peeking_next_by_clone! </span>{ [<span class="lifetime">'a</span>, T] ::std::option::Iter<<span class="lifetime">'a</span>, T> } |
| <span class="macro">peeking_next_by_clone! </span>{ [<span class="lifetime">'a</span>, T] ::std::result::Iter<<span class="lifetime">'a</span>, T> } |
| <span class="macro">peeking_next_by_clone! </span>{ [T] ::std::iter::Empty<T> } |
| <span class="attribute">#[cfg(feature = <span class="string">"use_alloc"</span>)] |
| </span><span class="macro">peeking_next_by_clone! </span>{ [<span class="lifetime">'a</span>, T] alloc::collections::linked_list::Iter<<span class="lifetime">'a</span>, T> } |
| <span class="attribute">#[cfg(feature = <span class="string">"use_alloc"</span>)] |
| </span><span class="macro">peeking_next_by_clone! </span>{ [<span class="lifetime">'a</span>, T] alloc::collections::vec_deque::Iter<<span class="lifetime">'a</span>, T> } |
| |
| <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>{ [I: Clone + PeekingNext + DoubleEndedIterator] |
| ::std::iter::Rev<I> } |
| </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> |
