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#[cfg(feature = "no_std")]
use std::prelude::*;
use std::cell::RefCell;
pub struct ImmutVecItem<T> {
prev: Option<usize>,
data: T
}
pub struct ImmutVec<'a, T> {
inner: &'a RefCell<Vec<ImmutVecItem<T>>>,
id: Option<usize>
}
impl<'a, T> Copy for ImmutVec<'a, T> {}
impl<'a, T> Clone for ImmutVec<'a, T> {
fn clone(&self) -> Self {
Self {
inner: self.inner,
id: self.id
}
}
}
impl<'a, T> ImmutVec<'a, T> {
pub fn new(inner: &'a RefCell<Vec<ImmutVecItem<T>>>) -> Self {
Self {
inner,
id: None
}
}
#[must_use = "push does nothing to the original vector"]
pub fn push(self, item: T) -> Self {
let mut inner = self.inner.borrow_mut();
let id = inner.len();
inner.push(ImmutVecItem {
prev: self.id,
data: item
});
Self {
id: Some(id),
..self
}
}
}
impl<'a, T: Clone> ImmutVec<'a, T> {
#[must_use = "pop does nothing to the original vector"]
pub fn pop(self) -> (Self, Option<T>) {
let inner = self.inner.borrow();
let id = match self.id {
None => return (self, None),
Some(id) => id
};
let item = &inner[id];
(Self {
id: item.prev,
..self
}, Some(item.data.clone()))
}
pub fn iter_rev(self) -> ImmutVecIter<'a, T> {
ImmutVecIter(self)
}
}
pub struct ImmutVecIter<'a, T: Clone>(ImmutVec<'a, T>);
impl<'a, T: Clone> Iterator for ImmutVecIter<'a, T> {
type Item = T;
fn next(&mut self) -> Option<Self::Item> {
let (new, item) = self.0.pop();
self.0 = new;
item
}
}