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use crate::{Entry, Slab};
// Building `Slab` from pairs (usize, T).
pub(crate) struct Builder<T> {
slab: Slab<T>,
vacant_list_broken: bool,
first_vacant_index: Option<usize>,
}
impl<T> Builder<T> {
pub(crate) fn with_capacity(capacity: usize) -> Self {
Self {
slab: Slab::with_capacity(capacity),
vacant_list_broken: false,
first_vacant_index: None,
}
}
pub(crate) fn pair(&mut self, key: usize, value: T) {
let slab = &mut self.slab;
if key < slab.entries.len() {
// iterator is not sorted, might need to recreate vacant list
if let Entry::Vacant(_) = slab.entries[key] {
self.vacant_list_broken = true;
slab.len += 1;
}
// if an element with this key already exists, replace it.
// This is consistent with HashMap and BtreeMap
slab.entries[key] = Entry::Occupied(value);
} else {
if self.first_vacant_index.is_none() && slab.entries.len() < key {
self.first_vacant_index = Some(slab.entries.len());
}
// insert holes as necessary
while slab.entries.len() < key {
// add the entry to the start of the vacant list
let next = slab.next;
slab.next = slab.entries.len();
slab.entries.push(Entry::Vacant(next));
}
slab.entries.push(Entry::Occupied(value));
slab.len += 1;
}
}
pub(crate) fn build(self) -> Slab<T> {
let mut slab = self.slab;
if slab.len == slab.entries.len() {
// no vacant entries, so next might not have been updated
slab.next = slab.entries.len();
} else if self.vacant_list_broken {
slab.recreate_vacant_list();
} else if let Some(first_vacant_index) = self.first_vacant_index {
let next = slab.entries.len();
match &mut slab.entries[first_vacant_index] {
Entry::Vacant(n) => *n = next,
_ => unreachable!(),
}
} else {
unreachable!()
}
slab
}
}
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