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-rw-r--r--third_party/rust/slab/src/builder.rs63
1 files changed, 63 insertions, 0 deletions
diff --git a/third_party/rust/slab/src/builder.rs b/third_party/rust/slab/src/builder.rs
new file mode 100644
index 0000000000..8e50a2016e
--- /dev/null
+++ b/third_party/rust/slab/src/builder.rs
@@ -0,0 +1,63 @@
+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
+ }
+}