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use std::cell::UnsafeCell;
use std::iter::FromIterator;
use std::ops::Index;
use stable_deref_trait::StableDeref;
pub struct FrozenVec<T> {
vec: UnsafeCell<Vec<T>>,
}
impl<T> FrozenVec<T> {
pub fn new() -> Self {
Self {
vec: UnsafeCell::new(Default::default()),
}
}
}
impl<T: StableDeref> FrozenVec<T> {
pub fn push(&self, val: T) {
unsafe {
let vec = self.vec.get();
(*vec).push(val)
}
}
pub fn get(&self, index: usize) -> Option<&T::Target> {
unsafe {
let vec = self.vec.get();
(*vec).get(index).map(|x| &**x)
}
}
pub fn len(&self) -> usize {
unsafe {
let vec = self.vec.get();
(*vec).len()
}
}
pub fn iter(&self) -> Iter<T> {
self.into_iter()
}
pub fn into_vec(self) -> Vec<T> {
self.vec.into_inner()
}
}
impl<T> Default for FrozenVec<T> {
fn default() -> Self {
FrozenVec::new()
}
}
impl<T> From<Vec<T>> for FrozenVec<T> {
fn from(vec: Vec<T>) -> Self {
Self {
vec: UnsafeCell::new(vec)
}
}
}
impl<T: StableDeref> Index<usize> for FrozenVec<T> {
type Output = T::Target;
fn index(&self, idx: usize) -> &T::Target {
self.get(idx)
.unwrap_or_else(|| panic!("index out of bounds: the len is {} but the index is {}", self.len(), idx))
}
}
impl<A> FromIterator<A> for FrozenVec<A> {
fn from_iter<T>(iter: T) -> Self
where
T: IntoIterator<Item = A> {
let vec: Vec<_> = iter.into_iter().collect();
vec.into()
}
}
pub struct Iter<'a, T> {
vec: &'a FrozenVec<T>,
idx: usize
}
impl<'a, T: StableDeref> Iterator for Iter<'a, T> {
type Item = &'a T::Target;
fn next(&mut self) -> Option<&'a T::Target> {
if let Some(ret) = self.vec.get(self.idx) {
self.idx += 1;
Some(ret)
} else {
None
}
}
}
impl<'a, T: StableDeref> IntoIterator for &'a FrozenVec<T> {
type Item = &'a T::Target;
type IntoIter = Iter<'a, T>;
fn into_iter(self) -> Iter<'a, T> {
Iter {
vec: self,
idx: 0
}
}
}
#[test]
fn test_iteration() {
let vec = vec!["a", "b", "c", "d"];
let frozen: FrozenVec<_> = vec.clone().into();
assert_eq!(vec, frozen.iter().collect::<Vec<_>>());
for (e1, e2) in vec.iter().zip(frozen.iter()) {
assert_eq!(*e1, e2);
}
assert_eq!(vec.len(), frozen.iter().count())
}