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use std::borrow::Borrow;
use std::cell::{Cell, UnsafeCell};
use std::collections::hash_map::RandomState;
use std::hash::{BuildHasher, Hash};
use std::iter::FromIterator;
use std::ops::Index;
use indexmap::IndexSet;
use stable_deref_trait::StableDeref;
/// Append-only version of `indexmap::IndexSet` where
/// insertion does not require mutable access
pub struct FrozenIndexSet<T, S = RandomState> {
set: UnsafeCell<IndexSet<T, S>>,
/// Eq/Hash implementations can have side-effects, and using Rc it is possible
/// for FrozenIndexSet::insert to be called on a key that itself contains the same
/// `FrozenIndexSet`, whose `eq` implementation also calls FrozenIndexSet::insert
///
/// We use this `in_use` flag to guard against any reentrancy.
in_use: Cell<bool>,
}
// safety: UnsafeCell implies !Sync
impl<T: Eq + Hash> FrozenIndexSet<T> {
pub fn new() -> Self {
Self::from(IndexSet::new())
}
}
impl<T: Eq + Hash + StableDeref, S: BuildHasher> FrozenIndexSet<T, S> {
// these should never return &T
// these should never delete any entries
pub fn insert(&self, value: T) -> &T::Target {
assert!(!self.in_use.get());
self.in_use.set(true);
let ret = unsafe {
let set = self.set.get();
let (index, _was_vacant) = (*set).insert_full(value);
&*(*set)[index]
};
self.in_use.set(false);
ret
}
// these should never return &T
// these should never delete any entries
pub fn insert_full(&self, value: T) -> (usize, &T::Target) {
assert!(!self.in_use.get());
self.in_use.set(true);
let ret = unsafe {
let set = self.set.get();
let (index, _was_vacant) = (*set).insert_full(value);
(index, &*(*set)[index])
};
self.in_use.set(false);
ret
}
// TODO implement in case the standard Entry API gets improved
// // TODO avoid double lookup
// pub fn entry<Q: ?Sized>(&self, value: &Q) -> Entry<T, Q>
// where Q: Hash + Equivalent<T> + ToOwned<Owned = T>
// {
// assert!(!self.in_use.get());
// self.in_use.set(true);
// unsafe {
// let set = self.set.get();
// match (*set).get_full(value) {
// Some((index, reference)) => {
// Entry::Occupied(OccupiedEntry {
// index,
// reference,
// set: &*set,
// })
// }
// None => {
// Entry::Vacant(VacantEntry {
// value: Cow::Borrowed(value),
// set: &*set,
// })
// }
// }
// }
// }
pub fn get<Q: ?Sized>(&self, k: &Q) -> Option<&T::Target>
where
T: Borrow<Q>,
Q: Hash + Eq,
{
assert!(!self.in_use.get());
self.in_use.set(true);
let ret = unsafe {
let set = self.set.get();
(*set).get(k).map(|x| &**x)
};
self.in_use.set(false);
ret
}
pub fn get_full<Q: ?Sized>(&self, k: &Q) -> Option<(usize, &T::Target)>
where
T: Borrow<Q>,
Q: Hash + Eq,
{
assert!(!self.in_use.get());
self.in_use.set(true);
let ret = unsafe {
let set = self.set.get();
(*set).get_full(k).map(|(i, x)| (i, &**x))
};
self.in_use.set(false);
ret
}
pub fn get_index(&self, index: usize) -> Option<&T::Target> {
assert!(!self.in_use.get());
self.in_use.set(true);
let ret = unsafe {
let set = self.set.get();
(*set).get_index(index).map(|r| &**r)
};
self.in_use.set(false);
ret
}
pub fn into_set(self) -> IndexSet<T, S> {
self.set.into_inner()
}
/// Get mutable access to the underlying [`IndexSet`].
///
/// This is safe, as it requires a `&mut self`, ensuring nothing is using
/// the 'frozen' contents.
pub fn as_mut(&mut self) -> &mut IndexSet<T, S> {
unsafe { &mut *self.set.get() }
}
// TODO add more
}
impl<T, S> From<IndexSet<T, S>> for FrozenIndexSet<T, S> {
fn from(set: IndexSet<T, S>) -> Self {
Self {
set: UnsafeCell::new(set),
in_use: Cell::new(false),
}
}
}
impl<T: Eq + Hash + StableDeref, S> Index<usize> for FrozenIndexSet<T, S> {
type Output = T::Target;
fn index(&self, idx: usize) -> &T::Target {
assert!(!self.in_use.get());
self.in_use.set(true);
let ret = unsafe {
let set = self.set.get();
&*(*set)[idx]
};
self.in_use.set(false);
ret
}
}
impl<T: Eq + Hash, S: Default + BuildHasher> FromIterator<T> for FrozenIndexSet<T, S> {
fn from_iter<U>(iter: U) -> Self
where
U: IntoIterator<Item = T>,
{
let set: IndexSet<_, _> = iter.into_iter().collect();
set.into()
}
}
impl<T: Eq + Hash, S: Default> Default for FrozenIndexSet<T, S> {
fn default() -> Self {
Self::from(IndexSet::default())
}
}
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