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use std::{
borrow::Borrow,
fmt::{self, Debug, Formatter},
hash::{Hash, Hasher},
ops::{Deref, Range},
sync::Arc,
};
/// A owned slice that is backed by an `Arc`.
#[derive(Clone)]
pub struct ArcSlice<T> {
data: *const [T],
arc: Arc<[T]>,
}
unsafe impl<T> Send for ArcSlice<T> {}
unsafe impl<T> Sync for ArcSlice<T> {}
impl<T> From<Arc<[T]>> for ArcSlice<T> {
fn from(arc: Arc<[T]>) -> Self {
Self {
data: &*arc as *const [T],
arc,
}
}
}
impl<T> From<Box<[T]>> for ArcSlice<T> {
fn from(b: Box<[T]>) -> Self {
Self::from(Arc::from(b))
}
}
impl<T> Deref for ArcSlice<T> {
type Target = [T];
fn deref(&self) -> &Self::Target {
unsafe { &*self.data }
}
}
impl<T> Borrow<[T]> for ArcSlice<T> {
fn borrow(&self) -> &[T] {
self
}
}
impl<T: Hash> Hash for ArcSlice<T> {
fn hash<H: Hasher>(&self, state: &mut H) {
self.deref().hash(state)
}
}
impl<T: PartialEq> PartialEq for ArcSlice<T> {
fn eq(&self, other: &Self) -> bool {
self.deref().eq(other.deref())
}
}
impl<T: Debug> Debug for ArcSlice<T> {
fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
Debug::fmt(&**self, f)
}
}
impl<T: Eq> Eq for ArcSlice<T> {}
impl<T> ArcSlice<T> {
/// Creates a new `ArcSlice` from a pointer to a slice and an `Arc`.
///
/// # Safety
///
/// The caller must ensure that the pointer is pointing to a valid slice that is kept alive by
/// the `Arc`.
pub unsafe fn new_unchecked(data: *const [T], arc: Arc<[T]>) -> Self {
Self { data, arc }
}
/// Get the backing arc
pub fn full_arc(this: &ArcSlice<T>) -> Arc<[T]> {
this.arc.clone()
}
/// Returns a new `ArcSlice` that points to a slice of the current slice.
pub fn slice(self, range: Range<usize>) -> ArcSlice<T> {
let data = &*self;
let data = &data[range] as *const [T];
Self {
data,
arc: self.arc,
}
}
}
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