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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-19 00:47:55 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-19 00:47:55 +0000
commit26a029d407be480d791972afb5975cf62c9360a6 (patch)
treef435a8308119effd964b339f76abb83a57c29483 /third_party/rust/itertools/src/peek_nth.rs
parentInitial commit. (diff)
downloadfirefox-26a029d407be480d791972afb5975cf62c9360a6.tar.xz
firefox-26a029d407be480d791972afb5975cf62c9360a6.zip
Adding upstream version 124.0.1.upstream/124.0.1
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'third_party/rust/itertools/src/peek_nth.rs')
-rw-r--r--third_party/rust/itertools/src/peek_nth.rs102
1 files changed, 102 insertions, 0 deletions
diff --git a/third_party/rust/itertools/src/peek_nth.rs b/third_party/rust/itertools/src/peek_nth.rs
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+++ b/third_party/rust/itertools/src/peek_nth.rs
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+use crate::size_hint;
+use crate::PeekingNext;
+use alloc::collections::VecDeque;
+use std::iter::Fuse;
+
+/// See [`peek_nth()`] for more information.
+#[derive(Clone, Debug)]
+pub struct PeekNth<I>
+where
+ I: Iterator,
+{
+ iter: Fuse<I>,
+ buf: VecDeque<I::Item>,
+}
+
+/// A drop-in replacement for [`std::iter::Peekable`] which adds a `peek_nth`
+/// method allowing the user to `peek` at a value several iterations forward
+/// without advancing the base iterator.
+///
+/// This differs from `multipeek` in that subsequent calls to `peek` or
+/// `peek_nth` will always return the same value until `next` is called
+/// (making `reset_peek` unnecessary).
+pub fn peek_nth<I>(iterable: I) -> PeekNth<I::IntoIter>
+where
+ I: IntoIterator,
+{
+ PeekNth {
+ iter: iterable.into_iter().fuse(),
+ buf: VecDeque::new(),
+ }
+}
+
+impl<I> PeekNth<I>
+where
+ I: Iterator,
+{
+ /// Works exactly like the `peek` method in `std::iter::Peekable`
+ pub fn peek(&mut self) -> Option<&I::Item> {
+ self.peek_nth(0)
+ }
+
+ /// Returns a reference to the `nth` value without advancing the iterator.
+ ///
+ /// # Examples
+ ///
+ /// Basic usage:
+ ///
+ /// ```rust
+ /// use itertools::peek_nth;
+ ///
+ /// let xs = vec![1,2,3];
+ /// let mut iter = peek_nth(xs.iter());
+ ///
+ /// assert_eq!(iter.peek_nth(0), Some(&&1));
+ /// assert_eq!(iter.next(), Some(&1));
+ ///
+ /// // The iterator does not advance even if we call `peek_nth` multiple times
+ /// assert_eq!(iter.peek_nth(0), Some(&&2));
+ /// assert_eq!(iter.peek_nth(1), Some(&&3));
+ /// assert_eq!(iter.next(), Some(&2));
+ ///
+ /// // Calling `peek_nth` past the end of the iterator will return `None`
+ /// assert_eq!(iter.peek_nth(1), None);
+ /// ```
+ pub fn peek_nth(&mut self, n: usize) -> Option<&I::Item> {
+ let unbuffered_items = (n + 1).saturating_sub(self.buf.len());
+
+ self.buf.extend(self.iter.by_ref().take(unbuffered_items));
+
+ self.buf.get(n)
+ }
+}
+
+impl<I> Iterator for PeekNth<I>
+where
+ I: Iterator,
+{
+ type Item = I::Item;
+
+ fn next(&mut self) -> Option<Self::Item> {
+ self.buf.pop_front().or_else(|| self.iter.next())
+ }
+
+ fn size_hint(&self) -> (usize, Option<usize>) {
+ size_hint::add_scalar(self.iter.size_hint(), self.buf.len())
+ }
+}
+
+impl<I> ExactSizeIterator for PeekNth<I> where I: ExactSizeIterator {}
+
+impl<I> PeekingNext for PeekNth<I>
+where
+ I: Iterator,
+{
+ fn peeking_next<F>(&mut self, accept: F) -> Option<Self::Item>
+ where
+ F: FnOnce(&Self::Item) -> bool,
+ {
+ self.peek().filter(|item| accept(item))?;
+ self.next()
+ }
+}