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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::IndexMap;
use stable_deref_trait::StableDeref;
/// Append-only version of `indexmap::IndexMap` where
/// insertion does not require mutable access
pub struct FrozenIndexMap<K, V, S = RandomState> {
map: UnsafeCell<IndexMap<K, V, S>>,
/// Eq/Hash implementations can have side-effects, and using Rc it is possible
/// for FrozenIndexMap::insert to be called on a key that itself contains the same
/// `FrozenIndexMap`, whose `eq` implementation also calls FrozenIndexMap::insert
///
/// We use this `in_use` flag to guard against any reentrancy.
in_use: Cell<bool>,
}
// safety: UnsafeCell implies !Sync
impl<K: Eq + Hash, V> FrozenIndexMap<K, V> {
pub fn new() -> Self {
Self {
map: UnsafeCell::new(Default::default()),
in_use: Cell::new(false),
}
}
}
impl<K: Eq + Hash, V: StableDeref, S: BuildHasher> FrozenIndexMap<K, V, S> {
// these should never return &K or &V
// these should never delete any entries
pub fn insert(&self, k: K, v: V) -> &V::Target {
assert!(!self.in_use.get());
self.in_use.set(true);
let ret = unsafe {
let map = self.map.get();
&*(*map).entry(k).or_insert(v)
};
self.in_use.set(false);
ret
}
// these should never return &K or &V
// these should never delete any entries
pub fn insert_full(&self, k: K, v: V) -> (usize, &V::Target) {
assert!(!self.in_use.get());
self.in_use.set(true);
let ret = unsafe {
let map = self.map.get();
let entry = (*map).entry(k);
let index = entry.index();
(index, &**entry.or_insert(v))
};
self.in_use.set(false);
ret
}
/// Returns a reference to the value corresponding to the key.
///
/// The key may be any borrowed form of the map's key type, but
/// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
/// the key type.
///
/// # Examples
///
/// ```
/// use elsa::FrozenIndexMap;
///
/// let map = FrozenIndexMap::new();
/// map.insert(1, Box::new("a"));
/// assert_eq!(map.get(&1), Some(&"a"));
/// assert_eq!(map.get(&2), None);
/// ```
pub fn get<Q: ?Sized>(&self, k: &Q) -> Option<&V::Target>
where
K: Borrow<Q>,
Q: Hash + Eq,
{
assert!(!self.in_use.get());
self.in_use.set(true);
let ret = unsafe {
let map = self.map.get();
(*map).get(k).map(|x| &**x)
};
self.in_use.set(false);
ret
}
pub fn get_index(&self, index: usize) -> Option<(&K::Target, &V::Target)>
where
K: StableDeref,
{
assert!(!self.in_use.get());
self.in_use.set(true);
let ret = unsafe {
let map = self.map.get();
(*map).get_index(index).map(|(k, v)| (&**k, &**v))
};
self.in_use.set(false);
ret
}
/// Applies a function to the owner of the value corresponding to the key (if any).
///
/// The key may be any borrowed form of the map's key type, but
/// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
/// the key type.
///
/// # Examples
///
/// ```
/// use elsa::FrozenIndexMap;
///
/// let map = FrozenIndexMap::new();
/// map.insert(1, Box::new("a"));
/// assert_eq!(map.map_get(&1, Clone::clone), Some(Box::new("a")));
/// assert_eq!(map.map_get(&2, Clone::clone), None);
/// ```
pub fn map_get<Q: ?Sized, T, F>(&self, k: &Q, f: F) -> Option<T>
where
K: Borrow<Q>,
Q: Hash + Eq,
F: FnOnce(&V) -> T,
{
assert!(!self.in_use.get());
self.in_use.set(true);
let ret = unsafe {
let map = self.map.get();
(*map).get(k).map(f)
};
self.in_use.set(false);
ret
}
pub fn into_map(self) -> IndexMap<K, V, S> {
self.map.into_inner()
}
/// Get mutable access to the underlying [`IndexMap`].
///
/// This is safe, as it requires a `&mut self`, ensuring nothing is using
/// the 'frozen' contents.
pub fn as_mut(&mut self) -> &mut IndexMap<K, V, S> {
unsafe { &mut *self.map.get() }
}
/// Returns true if the map contains no elements.
pub fn is_empty(&self) -> bool {
assert!(!self.in_use.get());
self.in_use.set(true);
let ret = unsafe {
let map = self.map.get();
(*map).is_empty()
};
self.in_use.set(false);
ret
}
}
impl<K, V, S> From<IndexMap<K, V, S>> for FrozenIndexMap<K, V, S> {
fn from(map: IndexMap<K, V, S>) -> Self {
Self {
map: UnsafeCell::new(map),
in_use: Cell::new(false),
}
}
}
impl<Q: ?Sized, K: Eq + Hash, V: StableDeref, S: BuildHasher> Index<&Q> for FrozenIndexMap<K, V, S>
where
Q: Eq + Hash,
K: Eq + Hash + Borrow<Q>,
V: StableDeref,
S: BuildHasher
{
type Output = V::Target;
/// # Examples
///
/// ```
/// use elsa::FrozenIndexMap;
///
/// let map = FrozenIndexMap::new();
/// map.insert(1, Box::new("a"));
/// assert_eq!(map[&1], "a");
/// ```
fn index(&self, idx: &Q) -> &V::Target {
self.get(&idx)
.expect("attempted to index FrozenIndexMap with unknown key")
}
}
impl<K: Eq + Hash, V, S: BuildHasher + Default> FromIterator<(K, V)> for FrozenIndexMap<K, V, S> {
fn from_iter<T>(iter: T) -> Self
where
T: IntoIterator<Item = (K, V)>,
{
let map: IndexMap<_, _, _> = iter.into_iter().collect();
map.into()
}
}
impl<K: Eq + Hash, V, S: Default> Default for FrozenIndexMap<K, V, S> {
fn default() -> Self {
Self {
map: UnsafeCell::new(Default::default()),
in_use: Cell::new(false),
}
}
}
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