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-rw-r--r--third_party/rust/itertools/src/with_position.rs100
1 files changed, 100 insertions, 0 deletions
diff --git a/third_party/rust/itertools/src/with_position.rs b/third_party/rust/itertools/src/with_position.rs
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+++ b/third_party/rust/itertools/src/with_position.rs
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+use std::iter::{Fuse,Peekable, FusedIterator};
+
+/// An iterator adaptor that wraps each element in an [`Position`].
+///
+/// Iterator element type is `Position<I::Item>`.
+///
+/// See [`.with_position()`](crate::Itertools::with_position) for more information.
+#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
+pub struct WithPosition<I>
+ where I: Iterator,
+{
+ handled_first: bool,
+ peekable: Peekable<Fuse<I>>,
+}
+
+impl<I> Clone for WithPosition<I>
+ where I: Clone + Iterator,
+ I::Item: Clone,
+{
+ clone_fields!(handled_first, peekable);
+}
+
+/// Create a new `WithPosition` iterator.
+pub fn with_position<I>(iter: I) -> WithPosition<I>
+ where I: Iterator,
+{
+ WithPosition {
+ handled_first: false,
+ peekable: iter.fuse().peekable(),
+ }
+}
+
+/// A value yielded by `WithPosition`.
+/// Indicates the position of this element in the iterator results.
+///
+/// See [`.with_position()`](crate::Itertools::with_position) for more information.
+#[derive(Copy, Clone, Debug, PartialEq)]
+pub enum Position<T> {
+ /// This is the first element.
+ First(T),
+ /// This is neither the first nor the last element.
+ Middle(T),
+ /// This is the last element.
+ Last(T),
+ /// This is the only element.
+ Only(T),
+}
+
+impl<T> Position<T> {
+ /// Return the inner value.
+ pub fn into_inner(self) -> T {
+ match self {
+ Position::First(x) |
+ Position::Middle(x) |
+ Position::Last(x) |
+ Position::Only(x) => x,
+ }
+ }
+}
+
+impl<I: Iterator> Iterator for WithPosition<I> {
+ type Item = Position<I::Item>;
+
+ fn next(&mut self) -> Option<Self::Item> {
+ match self.peekable.next() {
+ Some(item) => {
+ if !self.handled_first {
+ // Haven't seen the first item yet, and there is one to give.
+ self.handled_first = true;
+ // Peek to see if this is also the last item,
+ // in which case tag it as `Only`.
+ match self.peekable.peek() {
+ Some(_) => Some(Position::First(item)),
+ None => Some(Position::Only(item)),
+ }
+ } else {
+ // Have seen the first item, and there's something left.
+ // Peek to see if this is the last item.
+ match self.peekable.peek() {
+ Some(_) => Some(Position::Middle(item)),
+ None => Some(Position::Last(item)),
+ }
+ }
+ }
+ // Iterator is finished.
+ None => None,
+ }
+ }
+
+ fn size_hint(&self) -> (usize, Option<usize>) {
+ self.peekable.size_hint()
+ }
+}
+
+impl<I> ExactSizeIterator for WithPosition<I>
+ where I: ExactSizeIterator,
+{ }
+
+impl<I: Iterator> FusedIterator for WithPosition<I>
+{}