library/core/src/iter/adapters/copied.rs

   1 use crate::iter::adapters::{zip::try_get_unchecked, TrustedRandomAccess};
   2 use crate::iter::{FusedIterator, TrustedLen};
   3 use crate::ops::Try;
   4
   5 /// An iterator that copies the elements of an underlying iterator.
   6 ///
   7 /// This `struct` is created by the [`copied`] method on [`Iterator`]. See its
   8 /// documentation for more.
   9 ///
  10 /// [`copied`]: Iterator::copied
  11 /// [`Iterator`]: trait.Iterator.html
  12 #[stable(feature = "iter_copied", since = "1.36.0")]
  13 #[must_use = "iterators are lazy and do nothing unless consumed"]
  14 #[derive(Clone, Debug)]
  15 pub struct Copied<I> {
  16     it: I,
  17 }
  18
  19 impl<I> Copied<I> {
  20     pub(in crate::iter) fn new(it: I) -> Copied<I> {
  21         Copied { it }
  22     }
  23 }
  24
  25 fn copy_fold<T: Copy, Acc>(mut f: impl FnMut(Acc, T) -> Acc) -> impl FnMut(Acc, &T) -> Acc {
  26     move |acc, &elt| f(acc, elt)
  27 }
  28
  29 fn copy_try_fold<T: Copy, Acc, R>(mut f: impl FnMut(Acc, T) -> R) -> impl FnMut(Acc, &T) -> R {
  30     move |acc, &elt| f(acc, elt)
  31 }
  32
  33 #[stable(feature = "iter_copied", since = "1.36.0")]
  34 impl<'a, I, T: 'a> Iterator for Copied<I>
  35 where
  36     I: Iterator<Item = &'a T>,
  37     T: Copy,
  38 {
  39     type Item = T;
  40
  41     fn next(&mut self) -> Option<T> {
  42         self.it.next().copied()
  43     }
  44
  45     fn size_hint(&self) -> (usize, Option<usize>) {
  46         self.it.size_hint()
  47     }
  48
  49     fn try_fold<B, F, R>(&mut self, init: B, f: F) -> R
  50     where
  51         Self: Sized,
  52         F: FnMut(B, Self::Item) -> R,
  53         R: Try<Output = B>,
  54     {
  55         self.it.try_fold(init, copy_try_fold(f))
  56     }
  57
  58     fn fold<Acc, F>(self, init: Acc, f: F) -> Acc
  59     where
  60         F: FnMut(Acc, Self::Item) -> Acc,
  61     {
  62         self.it.fold(init, copy_fold(f))
  63     }
  64
  65     fn nth(&mut self, n: usize) -> Option<T> {
  66         self.it.nth(n).copied()
  67     }
  68
  69     fn last(self) -> Option<T> {
  70         self.it.last().copied()
  71     }
  72
  73     fn count(self) -> usize {
  74         self.it.count()
  75     }
  76
  77     unsafe fn __iterator_get_unchecked(&mut self, idx: usize) -> T
  78     where
  79         Self: TrustedRandomAccess,
  80     {
  81         // SAFETY: the caller must uphold the contract for
  82         // `Iterator::__iterator_get_unchecked`.
  83         *unsafe { try_get_unchecked(&mut self.it, idx) }
  84     }
  85 }
  86
  87 #[stable(feature = "iter_copied", since = "1.36.0")]
  88 impl<'a, I, T: 'a> DoubleEndedIterator for Copied<I>
  89 where
  90     I: DoubleEndedIterator<Item = &'a T>,
  91     T: Copy,
  92 {
  93     fn next_back(&mut self) -> Option<T> {
  94         self.it.next_back().copied()
  95     }
  96
  97     fn try_rfold<B, F, R>(&mut self, init: B, f: F) -> R
  98     where
  99         Self: Sized,
 100         F: FnMut(B, Self::Item) -> R,
 101         R: Try<Output = B>,
 102     {
 103         self.it.try_rfold(init, copy_try_fold(f))
 104     }
 105
 106     fn rfold<Acc, F>(self, init: Acc, f: F) -> Acc
 107     where
 108         F: FnMut(Acc, Self::Item) -> Acc,
 109     {
 110         self.it.rfold(init, copy_fold(f))
 111     }
 112 }
 113
 114 #[stable(feature = "iter_copied", since = "1.36.0")]
 115 impl<'a, I, T: 'a> ExactSizeIterator for Copied<I>
 116 where
 117     I: ExactSizeIterator<Item = &'a T>,
 118     T: Copy,
 119 {
 120     fn len(&self) -> usize {
 121         self.it.len()
 122     }
 123
 124     fn is_empty(&self) -> bool {
 125         self.it.is_empty()
 126     }
 127 }
 128
 129 #[stable(feature = "iter_copied", since = "1.36.0")]
 130 impl<'a, I, T: 'a> FusedIterator for Copied<I>
 131 where
 132     I: FusedIterator<Item = &'a T>,
 133     T: Copy,
 134 {
 135 }
 136
 137 #[doc(hidden)]
 138 #[unstable(feature = "trusted_random_access", issue = "none")]
 139 unsafe impl<I> TrustedRandomAccess for Copied<I>
 140 where
 141     I: TrustedRandomAccess,
 142 {
 143     const MAY_HAVE_SIDE_EFFECT: bool = I::MAY_HAVE_SIDE_EFFECT;
 144 }
 145
 146 #[stable(feature = "iter_copied", since = "1.36.0")]
 147 unsafe impl<'a, I, T: 'a> TrustedLen for Copied<I>
 148 where
 149     I: TrustedLen<Item = &'a T>,
 150     T: Copy,
 151 {
 152 }