owned_slice.rs

use std::borrow::Cow;

use bytemuck::{try_cast_slice, AnyBitPattern, NoUninit, PodCastError};
use heed_traits::{BytesDecode, BytesEncode};

use crate::CowSlice;

/// Describes a [`Vec`] of types that are totally owned (doesn't
/// hold any reference to the original slice).
///
/// If you need to store a type that doesn't depends on any
/// [memory alignment] and that can be big it is recommended
/// to use the [`UnalignedSlice`].
///
/// The [`CowType`] is recommended for borrowed types (types that holds
/// references to the original slice).
///
/// [memory alignment]: std::mem::align_of()
/// [`UnalignedSlice`]: crate::UnalignedSlice
/// [`CowType`]: crate::CowType
pub struct OwnedSlice<T>(std::marker::PhantomData<T>);

impl<'a, T: NoUninit> BytesEncode<'a> for OwnedSlice<T> {
    type EItem = [T];
    type Err = PodCastError;

    fn bytes_encode(item: &'a Self::EItem) -> Result<Cow<[u8]>, Self::Err> {
        try_cast_slice(item).map(Cow::Borrowed)
    }
}

impl<'a, T: AnyBitPattern + NoUninit> BytesDecode<'a> for OwnedSlice<T> {
    type DItem = Vec<T>;
    type Err = PodCastError;

    fn bytes_decode(bytes: &[u8]) -> Result<Self::DItem, Self::Err> {
        CowSlice::<T>::bytes_decode(bytes).map(Cow::into_owned)
    }
}

unsafe impl<T> Send for OwnedSlice<T> {}

unsafe impl<T> Sync for OwnedSlice<T> {}