1 files changed, 168 insertions, 0 deletions
diff --git a/library/core/src/iter/adapters/copied.rs b/library/core/src/iter/adapters/copied.rs
new file mode 100644
index 000000000..f9bfd77d7
--- /dev/null
+++ b/library/core/src/iter/adapters/copied.rs
@@ -0,0 +1,168 @@
+use crate::iter::adapters::{
+    zip::try_get_unchecked, TrustedRandomAccess, TrustedRandomAccessNoCoerce,
+};
+use crate::iter::{FusedIterator, TrustedLen};
+use crate::ops::Try;
+
+/// An iterator that copies the elements of an underlying iterator.
+///
+/// This `struct` is created by the [`copied`] method on [`Iterator`]. See its
+/// documentation for more.
+///
+/// [`copied`]: Iterator::copied
+/// [`Iterator`]: trait.Iterator.html
+#[stable(feature = "iter_copied", since = "1.36.0")]
+#[must_use = "iterators are lazy and do nothing unless consumed"]
+#[derive(Clone, Debug)]
+pub struct Copied<I> {
+    it: I,
+}
+
+impl<I> Copied<I> {
+    pub(in crate::iter) fn new(it: I) -> Copied<I> {
+        Copied { it }
+    }
+}
+
+fn copy_fold<T: Copy, Acc>(mut f: impl FnMut(Acc, T) -> Acc) -> impl FnMut(Acc, &T) -> Acc {
+    move |acc, &elt| f(acc, elt)
+}
+
+fn copy_try_fold<T: Copy, Acc, R>(mut f: impl FnMut(Acc, T) -> R) -> impl FnMut(Acc, &T) -> R {
+    move |acc, &elt| f(acc, elt)
+}
+
+#[stable(feature = "iter_copied", since = "1.36.0")]
+impl<'a, I, T: 'a> Iterator for Copied<I>
+where
+    I: Iterator<Item = &'a T>,
+    T: Copy,
+{
+    type Item = T;
+
+    fn next(&mut self) -> Option<T> {
+        self.it.next().copied()
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.it.size_hint()
+    }
+
+    fn try_fold<B, F, R>(&mut self, init: B, f: F) -> R
+    where
+        Self: Sized,
+        F: FnMut(B, Self::Item) -> R,
+        R: Try<Output = B>,
+    {
+        self.it.try_fold(init, copy_try_fold(f))
+    }
+
+    fn fold<Acc, F>(self, init: Acc, f: F) -> Acc
+    where
+        F: FnMut(Acc, Self::Item) -> Acc,
+    {
+        self.it.fold(init, copy_fold(f))
+    }
+
+    fn nth(&mut self, n: usize) -> Option<T> {
+        self.it.nth(n).copied()
+    }
+
+    fn last(self) -> Option<T> {
+        self.it.last().copied()
+    }
+
+    fn count(self) -> usize {
+        self.it.count()
+    }
+
+    #[inline]
+    fn advance_by(&mut self, n: usize) -> Result<(), usize> {
+        self.it.advance_by(n)
+    }
+
+    unsafe fn __iterator_get_unchecked(&mut self, idx: usize) -> T
+    where
+        Self: TrustedRandomAccessNoCoerce,
+    {
+        // SAFETY: the caller must uphold the contract for
+        // `Iterator::__iterator_get_unchecked`.
+        *unsafe { try_get_unchecked(&mut self.it, idx) }
+    }
+}
+
+#[stable(feature = "iter_copied", since = "1.36.0")]
+impl<'a, I, T: 'a> DoubleEndedIterator for Copied<I>
+where
+    I: DoubleEndedIterator<Item = &'a T>,
+    T: Copy,
+{
+    fn next_back(&mut self) -> Option<T> {
+        self.it.next_back().copied()
+    }
+
+    fn try_rfold<B, F, R>(&mut self, init: B, f: F) -> R
+    where
+        Self: Sized,
+        F: FnMut(B, Self::Item) -> R,
+        R: Try<Output = B>,
+    {
+        self.it.try_rfold(init, copy_try_fold(f))
+    }
+
+    fn rfold<Acc, F>(self, init: Acc, f: F) -> Acc
+    where
+        F: FnMut(Acc, Self::Item) -> Acc,
+    {
+        self.it.rfold(init, copy_fold(f))
+    }
+
+    #[inline]
+    fn advance_back_by(&mut self, n: usize) -> Result<(), usize> {
+        self.it.advance_back_by(n)
+    }
+}
+
+#[stable(feature = "iter_copied", since = "1.36.0")]
+impl<'a, I, T: 'a> ExactSizeIterator for Copied<I>
+where
+    I: ExactSizeIterator<Item = &'a T>,
+    T: Copy,
+{
+    fn len(&self) -> usize {
+        self.it.len()
+    }
+
+    fn is_empty(&self) -> bool {
+        self.it.is_empty()
+    }
+}
+
+#[stable(feature = "iter_copied", since = "1.36.0")]
+impl<'a, I, T: 'a> FusedIterator for Copied<I>
+where
+    I: FusedIterator<Item = &'a T>,
+    T: Copy,
+{
+}
+
+#[doc(hidden)]
+#[unstable(feature = "trusted_random_access", issue = "none")]
+unsafe impl<I> TrustedRandomAccess for Copied<I> where I: TrustedRandomAccess {}
+
+#[doc(hidden)]
+#[unstable(feature = "trusted_random_access", issue = "none")]
+unsafe impl<I> TrustedRandomAccessNoCoerce for Copied<I>
+where
+    I: TrustedRandomAccessNoCoerce,
+{
+    const MAY_HAVE_SIDE_EFFECT: bool = I::MAY_HAVE_SIDE_EFFECT;
+}
+
+#[stable(feature = "iter_copied", since = "1.36.0")]
+unsafe impl<'a, I, T: 'a> TrustedLen for Copied<I>
+where
+    I: TrustedLen<Item = &'a T>,
+    T: Copy,
+{
+}