| 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(), |
| } |
| } |
| |
| /// The first component of the 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 { |
| /// This is the first element. |
| First, |
| /// This is neither the first nor the last element. |
| Middle, |
| /// This is the last element. |
| Last, |
| /// This is the only element. |
| Only, |
| } |
| |
| 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> |
| {} |