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use alloc::vec::Vec;
use crate::size_hint;
/// An iterator adaptor that allows putting multiple
/// items in front of the iterator.
///
/// Iterator element type is `I::Item`.
#[derive(Debug, Clone)]
pub struct PutBackN<I: Iterator> {
top: Vec<I::Item>,
iter: I,
}
/// Create an iterator where you can put back multiple values to the front
/// of the iteration.
///
/// Iterator element type is `I::Item`.
pub fn put_back_n<I>(iterable: I) -> PutBackN<I::IntoIter>
where I: IntoIterator
{
PutBackN {
top: Vec::new(),
iter: iterable.into_iter(),
}
}
impl<I: Iterator> PutBackN<I> {
/// Puts x in front of the iterator.
/// The values are yielded in order of the most recently put back
/// values first.
///
/// ```rust
/// use itertools::put_back_n;
///
/// let mut it = put_back_n(1..5);
/// it.next();
/// it.put_back(1);
/// it.put_back(0);
///
/// assert!(itertools::equal(it, 0..5));
/// ```
#[inline]
pub fn put_back(&mut self, x: I::Item) {
self.top.push(x);
}
}
impl<I: Iterator> Iterator for PutBackN<I> {
type Item = I::Item;
#[inline]
fn next(&mut self) -> Option<Self::Item> {
self.top.pop().or_else(|| self.iter.next())
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
size_hint::add_scalar(self.iter.size_hint(), self.top.len())
}
}