1 use std::iter::{Fuse,Peekable};
2
3 /// An iterator adaptor that wraps each element in an [`Position`](../enum.Position.html).
4 ///
5 /// Iterator element type is `Position<I::Item>`.
6 ///
7 /// See [`.with_position()`](../trait.Itertools.html#method.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.
with_position<I>(iter: I) -> WithPosition<I> where I: Iterator,24 pub fn with_position<I>(iter: I) -> WithPosition<I>
25 where I: Iterator,
26 {
27 WithPosition {
28 handled_first: false,
29 peekable: iter.fuse().peekable(),
30 }
31 }
32
33 /// A value yielded by `WithPosition`.
34 /// Indicates the position of this element in the iterator results.
35 ///
36 /// See [`.with_position()`](trait.Itertools.html#method.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.
into_inner(self) -> T51 pub fn into_inner(self) -> T {
52 match self {
53 Position::First(x) |
54 Position::Middle(x) |
55 Position::Last(x) |
56 Position::Only(x) => x,
57 }
58 }
59 }
60
61 impl<I: Iterator> Iterator for WithPosition<I> {
62 type Item = Position<I::Item>;
63
next(&mut self) -> Option<Self::Item>64 fn next(&mut self) -> Option<Self::Item> {
65 match self.peekable.next() {
66 Some(item) => {
67 if !self.handled_first {
68 // Haven't seen the first item yet, and there is one to give.
69 self.handled_first = true;
70 // Peek to see if this is also the last item,
71 // in which case tag it as `Only`.
72 match self.peekable.peek() {
73 Some(_) => Some(Position::First(item)),
74 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 match self.peekable.peek() {
80 Some(_) => Some(Position::Middle(item)),
81 None => Some(Position::Last(item)),
82 }
83 }
84 }
85 // Iterator is finished.
86 None => None,
87 }
88 }
89
size_hint(&self) -> (usize, Option<usize>)90 fn size_hint(&self) -> (usize, Option<usize>) {
91 self.peekable.size_hint()
92 }
93 }
94
95 impl<I> ExactSizeIterator for WithPosition<I>
96 where I: ExactSizeIterator,
97 { }
98