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use std::iter::{ExactSizeIterator, FusedIterator};
use crate::arena::{Arena, Index};
pub struct Drain<'a, T> {
pub(crate) arena: &'a mut Arena<T>,
pub(crate) slot: u32,
}
impl<'a, T> Iterator for Drain<'a, T> {
type Item = (Index, T);
fn next(&mut self) -> Option<Self::Item> {
loop {
if self.arena.is_empty() {
return None;
}
let slot = self.slot;
self.slot = self
.slot
.checked_add(1)
.unwrap_or_else(|| panic!("Overflowed u32 trying to drain 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<'a, T> FusedIterator for Drain<'a, T> {}
impl<'a, T> ExactSizeIterator for Drain<'a, T> {}
#[cfg(test)]
mod test {
use crate::Arena;
use std::collections::HashSet;
#[test]
fn drain() {
let mut arena = Arena::with_capacity(2);
let one = arena.insert(1);
let two = arena.insert(2);
let mut drained_pairs = HashSet::new();
let mut drain = arena.drain();
assert_eq!(drain.size_hint(), (2, Some(2)));
drained_pairs.insert(drain.next().unwrap());
assert_eq!(drain.size_hint(), (1, Some(1)));
drained_pairs.insert(drain.next().unwrap());
assert_eq!(drain.size_hint(), (0, Some(0)));
assert_eq!(drain.next(), None);
assert_eq!(drain.next(), None);
assert_eq!(drain.size_hint(), (0, Some(0)));
assert_eq!(arena.len(), 0);
assert_eq!(arena.capacity(), 2);
assert_eq!(drained_pairs.len(), 2);
assert!(drained_pairs.contains(&(one, 1)));
assert!(drained_pairs.contains(&(two, 2)));
let one_prime = arena.insert(1);
let two_prime = arena.insert(2);
assert_eq!(arena.len(), 2);
assert_eq!(arena.capacity(), 2);
assert_eq!(arena.get(one_prime), Some(&1));
assert_eq!(arena.get(two_prime), Some(&2));
assert_eq!(arena.get(one), None);
assert_eq!(arena.get(two), None);
}
}