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use core::fmt;
use core::iter::{FusedIterator, TrustedLen};

use super::VecDeque;

/// `VecDeque` 元素上的拥有的迭代器。
///
/// 该 `struct` 是通过 [`VecDeque`] (由 `IntoIterator` trait 提供) 上的 [`into_iter`] 方法创建的。
/// 有关更多信息，请参见其文档。
///
/// [`into_iter`]: VecDeque::into_iter
#[derive(Clone)]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct IntoIter<T> {
    pub(crate) inner: VecDeque<T>,
}

#[stable(feature = "collection_debug", since = "1.17.0")]
impl<T: fmt::Debug> fmt::Debug for IntoIter<T> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_tuple("IntoIter").field(&self.inner).finish()
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<T> Iterator for IntoIter<T> {
    type Item = T;

    #[inline]
    fn next(&mut self) -> Option<T> {
        self.inner.pop_front()
    }

    #[inline]
    fn size_hint(&self) -> (usize, Option<usize>) {
        let len = self.inner.len();
        (len, Some(len))
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<T> DoubleEndedIterator for IntoIter<T> {
    #[inline]
    fn next_back(&mut self) -> Option<T> {
        self.inner.pop_back()
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<T> ExactSizeIterator for IntoIter<T> {
    fn is_empty(&self) -> bool {
        self.inner.is_empty()
    }
}

#[stable(feature = "fused", since = "1.26.0")]
impl<T> FusedIterator for IntoIter<T> {}

#[unstable(feature = "trusted_len", issue = "37572")]
unsafe impl<T> TrustedLen for IntoIter<T> {}