itertools/
pad_tail.rs

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1use std::iter::Fuse;
2use size_hint;
3
4/// An iterator adaptor that pads a sequence to a minimum length by filling
5/// missing elements using a closure.
6///
7/// Iterator element type is `I::Item`.
8///
9/// See [`.pad_using()`](../trait.Itertools.html#method.pad_using) for more information.
10#[derive(Clone)]
11#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
12pub struct PadUsing<I, F> {
13    iter: Fuse<I>,
14    min: usize,
15    pos: usize,
16    filler: F,
17}
18
19/// Create a new **PadUsing** iterator.
20pub fn pad_using<I, F>(iter: I, min: usize, filler: F) -> PadUsing<I, F>
21    where I: Iterator,
22          F: FnMut(usize) -> I::Item
23{
24    PadUsing {
25        iter: iter.fuse(),
26        min: min,
27        pos: 0,
28        filler: filler,
29    }
30}
31
32impl<I, F> Iterator for PadUsing<I, F>
33    where I: Iterator,
34          F: FnMut(usize) -> I::Item
35{
36    type Item = I::Item;
37
38    #[inline]
39    fn next(&mut self) -> Option<I::Item> {
40        match self.iter.next() {
41            None => {
42                if self.pos < self.min {
43                    let e = Some((self.filler)(self.pos));
44                    self.pos += 1;
45                    e
46                } else {
47                    None
48                }
49            },
50            e => {
51                self.pos += 1;
52                e
53            }
54        }
55    }
56
57    fn size_hint(&self) -> (usize, Option<usize>) {
58        let tail = self.min.saturating_sub(self.pos);
59        size_hint::max(self.iter.size_hint(), (tail, Some(tail)))
60    }
61}
62
63impl<I, F> DoubleEndedIterator for PadUsing<I, F>
64    where I: DoubleEndedIterator + ExactSizeIterator,
65          F: FnMut(usize) -> I::Item
66{
67    fn next_back(&mut self) -> Option<I::Item> {
68        if self.min == 0 {
69            self.iter.next_back()
70        } else if self.iter.len() >= self.min {
71            self.min -= 1;
72            self.iter.next_back()
73        } else {
74            self.min -= 1;
75            Some((self.filler)(self.min))
76        }
77    }
78}
79
80impl<I, F> ExactSizeIterator for PadUsing<I, F>
81    where I: ExactSizeIterator,
82          F: FnMut(usize) -> I::Item
83{}
itertools/pad_tail.rs

itertools/
pad_tail.rs
