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use std::iter::{ExactSizeIterator, FusedIterator};
use crate::arena::{Arena, Index};
/// Iterator typed used when an Arena is turned [`IntoIterator`][IntoIterator].
pub struct IntoIter<T> {
pub(crate) arena: Arena<T>,
pub(crate) slot: u32,
}
impl<T> Iterator for IntoIter<T> {
type Item = (Index, T);
fn next(&mut self) -> Option<Self::Item> {
loop {
// If there are no entries remaining in the arena, we should always
// return None. Using this check instead of comparing with the
// arena's size allows us to skip any trailing empty entries.
if self.arena.is_empty() {
return None;
}
// slot may overflow if the arena's underlying storage contains more
// than 2^32 elements, but its internal length value was not
// changed, as it overflowing would panic before reaching this code.
let slot = self.slot;
self.slot = self
.slot
.checked_add(1)
.unwrap_or_else(|| panic!("Overflowed u32 trying to into_iter Arena"));
// If this entry is occupied, this method will mark it as an empty.
// Otherwise, we'll continue looping until we've removed all
// occupied entries from the arena.
if let Some((index, value)) = self.arena.remove_entry_by_slot(slot) {
return Some((index, value));
}
}
}
fn size_hint(&self) -> (usize, Option<usize>) {
(self.arena.len(), Some(self.arena.len()))
}
}
impl<T> FusedIterator for IntoIter<T> {}
impl<T> ExactSizeIterator for IntoIter<T> {}
#[cfg(test)]
mod test {
use crate::Arena;
use std::collections::HashSet;
#[test]
fn into_iter() {
let mut arena = Arena::with_capacity(2);
let one = arena.insert(1);
let two = arena.insert(2);
let mut pairs = HashSet::new();
let mut into_iter = arena.into_iter();
assert_eq!(into_iter.size_hint(), (2, Some(2)));
pairs.insert(into_iter.next().unwrap());
assert_eq!(into_iter.size_hint(), (1, Some(1)));
pairs.insert(into_iter.next().unwrap());
assert_eq!(into_iter.size_hint(), (0, Some(0)));
assert_eq!(into_iter.next(), None);
assert_eq!(into_iter.next(), None);
assert_eq!(into_iter.size_hint(), (0, Some(0)));
assert_eq!(pairs.len(), 2);
assert!(pairs.contains(&(one, 1)));
assert!(pairs.contains(&(two, 2)));
}
}
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