/rust/registry/src/index.crates.io-1949cf8c6b5b557f/itertools-0.10.5/src/with_position.rs

Source
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> 
{}

Line	Count	Source
1		use std::iter::{Fuse,Peekable, FusedIterator};
2
3		/// An iterator adaptor that wraps each element in an [`Position`].
4		///
5		/// Iterator element type is `Position<I::Item>`.
6		///
7		/// See [`.with_position()`](crate::Itertools::with_position) for more information.
8		#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
9		pub struct WithPosition<I>
10		where I: Iterator,
11		{
12		handled_first: bool,
13		peekable: Peekable<Fuse<I>>,
14		}
15
16		impl<I> Clone for WithPosition<I>
17		where I: Clone + Iterator,
18		I::Item: Clone,
19		{
20		clone_fields!(handled_first, peekable);
21		}
22
23		/// Create a new `WithPosition` iterator.
24	0	pub fn with_position<I>(iter: I) -> WithPosition<I>
25	0	where I: Iterator,
26		{
27	0	WithPosition {
28	0	handled_first: false,
29	0	peekable: iter.fuse().peekable(),
30	0	}
31	0	}
32
33		/// A value yielded by `WithPosition`.
34		/// Indicates the position of this element in the iterator results.
35		///
36		/// See [`.with_position()`](crate::Itertools::with_position) for more information.
37		#[derive(Copy, Clone, Debug, PartialEq)]
38		pub enum Position<T> {
39		/// This is the first element.
40		First(T),
41		/// This is neither the first nor the last element.
42		Middle(T),
43		/// This is the last element.
44		Last(T),
45		/// This is the only element.
46		Only(T),
47		}
48
49		impl<T> Position<T> {
50		/// Return the inner value.
51	0	pub fn into_inner(self) -> T {
52	0	match self {
53	0	Position::First(x) \|
54	0	Position::Middle(x) \|
55	0	Position::Last(x) \|
56	0	Position::Only(x) => x,
57		}
58	0	}
59		}
60
61		impl<I: Iterator> Iterator for WithPosition<I> {
62		type Item = Position<I::Item>;
63
64	0	fn next(&mut self) -> Option<Self::Item> {
65	0	match self.peekable.next() {
66	0	Some(item) => {
67	0	if !self.handled_first {
68		// Haven't seen the first item yet, and there is one to give.
69	0	self.handled_first = true;
70		// Peek to see if this is also the last item,
71		// in which case tag it as `Only`.
72	0	match self.peekable.peek() {
73	0	Some(_) => Some(Position::First(item)),
74	0	None => Some(Position::Only(item)),
75		}
76		} else {
77		// Have seen the first item, and there's something left.
78		// Peek to see if this is the last item.
79	0	match self.peekable.peek() {
80	0	Some(_) => Some(Position::Middle(item)),
81	0	None => Some(Position::Last(item)),
82		}
83		}
84		}
85		// Iterator is finished.
86	0	None => None,
87		}
88	0	}
89
90	0	fn size_hint(&self) -> (usize, Option<usize>) {
91	0	self.peekable.size_hint()
92	0	}
93		}
94
95		impl<I> ExactSizeIterator for WithPosition<I>
96		where I: ExactSizeIterator,
97		{ }
98
99		impl<I: Iterator> FusedIterator for WithPosition<I>
100		{}

Coverage Report

Created: 2026-09-04 06:48