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