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use std::collections::HashMap;
pub struct SlotMap<T> {
bitmap: u64,
map: HashMap<u32, T>,
}
impl<T> SlotMap<T> {
pub fn new() -> Self {
Self {
bitmap: u64::MAX,
map: HashMap::new(),
}
}
pub fn insert(&mut self, value: T) -> Option<u32> {
let slot = self.get_free_slot()?;
self.map.insert(slot, value);
self.use_slot(slot);
Some(slot)
}
pub fn remove(&mut self, slot: u32) -> Option<T> {
let value = self.map.remove(&slot)?;
self.release_slot(slot);
Some(value)
}
pub fn get(&self, slot: u32) -> Option<&T> {
self.map.get(&slot)
}
pub fn get_mut(&mut self, slot: u32) -> Option<&mut T> {
self.map.get_mut(&slot)
}
fn get_free_slot(&self) -> Option<u32> {
let leading_zeros = self.bitmap.leading_zeros();
if leading_zeros > 63 {
None
} else {
Some(63 - leading_zeros)
}
}
fn use_slot(&mut self, slot: u32) {
let mask = u64::MAX;
println!("{:0b}", self.bitmap);
self.bitmap &= !(1 << slot) & mask;
}
fn release_slot(&mut self, slot: u32) {
self.bitmap |= 1 << slot;
}
}
#[test]
fn releases_a_slot_after_removal() {
let mut slot_map = SlotMap::new();
assert_eq!(slot_map.insert(1), Some(63));
assert_eq!(slot_map.insert(2), Some(62));
assert_eq!(slot_map.insert(3), Some(61));
assert_eq!(slot_map.remove(&62), Some(2));
assert_eq!(slot_map.insert(4), Some(62));
assert_eq!(slot_map.insert(5), Some(60));
}
#[test]
fn uses_all_available_slots() {
let mut slot_map = SlotMap::new();
for x in 0..64 {
assert_eq!(slot_map.insert(0), Some(63 - x));
}
assert_eq!(slot_map.insert(0), None);
assert_eq!(slot_map.remove(&43), Some(0));
assert_eq!(slot_map.insert(0), Some(43));
}
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