vendor/itertools/src/pad_tail.rs

   1 use crate::size_hint;
   2 use std::iter::{Fuse, FusedIterator};
   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()`](crate::Itertools::pad_using) for more information.
  10 #[derive(Clone)]
  11 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
  12 pub struct PadUsing<I, F> {
  13     iter: Fuse<I>,
  14     min: usize,
  15     pos: usize,
  16     filler: F,
  17 }
  18
  19 impl<I, F> std::fmt::Debug for PadUsing<I, F>
  20 where
  21     I: std::fmt::Debug,
  22 {
  23     debug_fmt_fields!(PadUsing, iter, min, pos);
  24 }
  25
  26 /// Create a new `PadUsing` iterator.
  27 pub fn pad_using<I, F>(iter: I, min: usize, filler: F) -> PadUsing<I, F>
  28 where
  29     I: Iterator,
  30     F: FnMut(usize) -> I::Item,
  31 {
  32     PadUsing {
  33         iter: iter.fuse(),
  34         min,
  35         pos: 0,
  36         filler,
  37     }
  38 }
  39
  40 impl<I, F> Iterator for PadUsing<I, F>
  41 where
  42     I: Iterator,
  43     F: FnMut(usize) -> I::Item,
  44 {
  45     type Item = I::Item;
  46
  47     #[inline]
  48     fn next(&mut self) -> Option<Self::Item> {
  49         match self.iter.next() {
  50             None => {
  51                 if self.pos < self.min {
  52                     let e = Some((self.filler)(self.pos));
  53                     self.pos += 1;
  54                     e
  55                 } else {
  56                     None
  57                 }
  58             }
  59             e => {
  60                 self.pos += 1;
  61                 e
  62             }
  63         }
  64     }
  65
  66     fn size_hint(&self) -> (usize, Option<usize>) {
  67         let tail = self.min.saturating_sub(self.pos);
  68         size_hint::max(self.iter.size_hint(), (tail, Some(tail)))
  69     }
  70 }
  71
  72 impl<I, F> DoubleEndedIterator for PadUsing<I, F>
  73 where
  74     I: DoubleEndedIterator + ExactSizeIterator,
  75     F: FnMut(usize) -> I::Item,
  76 {
  77     fn next_back(&mut self) -> Option<Self::Item> {
  78         if self.min == 0 {
  79             self.iter.next_back()
  80         } else if self.iter.len() >= self.min {
  81             self.min -= 1;
  82             self.iter.next_back()
  83         } else {
  84             self.min -= 1;
  85             Some((self.filler)(self.min))
  86         }
  87     }
  88 }
  89
  90 impl<I, F> ExactSizeIterator for PadUsing<I, F>
  91 where
  92     I: ExactSizeIterator,
  93     F: FnMut(usize) -> I::Item,
  94 {
  95 }
  96
  97 impl<I, F> FusedIterator for PadUsing<I, F>
  98 where
  99     I: FusedIterator,
 100     F: FnMut(usize) -> I::Item,
 101 {
 102 }