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    use crate::iter::{FusedIterator, TrustedLen};

    /// Creates a new iterator that endlessly repeats a single element.
    ///
    /// The `repeat()` function repeats a single value over and over again.
    ///
    /// Infinite iterators like `repeat()` are often used with adapters like
    /// [`Iterator::take()`], in order to make them finite.
    ///
    /// If the element type of the iterator you need does not implement `Clone`,
    /// or if you do not want to keep the repeated element in memory, you can
    /// instead use the [`repeat_with()`] function.
    ///
    /// [`repeat_with()`]: crate::iter::repeat_with
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```
    /// use std::iter;
    ///
    /// // the number four 4ever:
    /// let mut fours = iter::repeat(4);
    ///
    /// assert_eq!(Some(4), fours.next());
    /// assert_eq!(Some(4), fours.next());
    /// assert_eq!(Some(4), fours.next());
    /// assert_eq!(Some(4), fours.next());
    /// assert_eq!(Some(4), fours.next());
    ///
    /// // yup, still four
    /// assert_eq!(Some(4), fours.next());
    /// ```
    ///
    /// Going finite with [`Iterator::take()`]:
    ///
    /// ```
    /// use std::iter;
    ///
    /// // that last example was too many fours. Let's only have four fours.
    /// let mut four_fours = iter::repeat(4).take(4);
    ///
    /// assert_eq!(Some(4), four_fours.next());
    /// assert_eq!(Some(4), four_fours.next());
    /// assert_eq!(Some(4), four_fours.next());
    /// assert_eq!(Some(4), four_fours.next());
    ///
    /// // ... and now we're done
    /// assert_eq!(None, four_fours.next());
    /// ```
    #[inline]
    #[stable(feature = "rust1", since = "1.0.0")]
    pub fn repeat<T: Clone>(elt: T) -> Repeat<T> {
        Repeat { element: elt }
    }

    /// An iterator that repeats an element endlessly.
    ///
    /// This `struct` is created by the [`repeat()`] function. See its documentation for more.
    #[derive(Clone, Debug)]
    #[stable(feature = "rust1", since = "1.0.0")]
    pub struct Repeat<A> {
        element: A,
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl<A: Clone> Iterator for Repeat<A> {
        type Item = A;

        #[inline]
        fn next(&mut self) -> Option<A> {
            Some(self.element.clone())
        }
        #[inline]
        fn size_hint(&self) -> (usize, Option<usize>) {
            (usize::MAX, None)
        }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl<A: Clone> DoubleEndedIterator for Repeat<A> {
        #[inline]
        fn next_back(&mut self) -> Option<A> {
            Some(self.element.clone())
        }
    }

    #[stable(feature = "fused", since = "1.26.0")]
    impl<A: Clone> FusedIterator for Repeat<A> {}

    #[unstable(feature = "trusted_len", issue = "37572")]
    unsafe impl<A: Clone> TrustedLen for Repeat<A> {}