arc-slice 0.1.0

Shared memory slices
Documentation 
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use std::{
    mem, ptr,
    sync::{
        atomic::{AtomicBool, Ordering},
        Arc,
    },
};

use arc_slice::{layout::BoxedSliceLayout, ArcBytes};

// empty vec subslices doesn't trigger promotion to an arc, so it can still be downcast
#[test]
fn empty_vec_subslices() {
    let mut bytes = ArcBytes::<BoxedSliceLayout>::from(vec![0, 1, 2, 3]);
    let clone1 = bytes.split_to(0);
    assert_eq!(clone1.as_ptr(), bytes.as_ptr());
    let clone2 = bytes.split_off(bytes.len());
    assert_eq!(clone2.as_ptr(), bytes[bytes.len()..].as_ptr());
    let clone3 = bytes.subslice(1..1);
    assert_eq!(clone3.as_ptr(), bytes[1..].as_ptr());
    let mut clone4 = bytes.split_off(0);
    assert_eq!(bytes.as_ptr(), bytes[..].as_ptr());
    mem::swap(&mut clone4, &mut bytes);
    let mut clone5 = bytes.split_to(bytes.len());
    assert_eq!(bytes.as_ptr(), bytes[..].as_ptr());
    mem::swap(&mut clone5, &mut bytes);
    assert_eq!(bytes.try_into_buffer::<Vec<u8>>().unwrap(), [0, 1, 2, 3]);
}

// into_vec reuse the internal vector even if in subslice case
#[test]
fn into_vec() {
    let vec = vec![0, 1, 2, 3];
    let vec_ptr = vec.as_ptr();

    let bytes = ArcBytes::<BoxedSliceLayout>::from(vec);
    let vec = bytes.try_into_buffer::<Vec<u8>>().unwrap();
    assert_eq!(vec.as_ptr(), vec_ptr);

    let mut bytes = ArcBytes::<BoxedSliceLayout>::from(vec);
    bytes.advance(2);
    let vec = bytes.try_into_buffer::<Vec<u8>>().unwrap();
    assert_eq!(vec, [2, 3]);
    assert_eq!(vec.as_ptr(), vec_ptr);

    let mut bytes = ArcBytes::<BoxedSliceLayout>::from(vec);
    bytes.truncate(1);
    let vec = bytes.try_into_buffer::<Vec<u8>>().unwrap();
    assert_eq!(vec, [2]);
    assert_eq!(vec.as_ptr(), vec_ptr);
}

#[derive(Default, Clone)]
struct Metadata {
    dropped: Arc<AtomicBool>,
}

impl Drop for Metadata {
    fn drop(&mut self) {
        self.dropped.store(true, Ordering::Relaxed);
    }
}

// metadata can be downcast, and is dropped when the slice is dropped
#[test]
fn metadata() {
    let metadata = Metadata::default();
    let bytes = ArcBytes::<BoxedSliceLayout>::from_buffer_with_metadata(vec![42], metadata.clone());
    assert!(bytes.metadata::<()>().is_none());
    assert!(bytes.metadata::<Metadata>().is_some());

    let clone = bytes.clone();
    assert!(clone.metadata::<()>().is_none());
    assert!(clone.metadata::<Metadata>().is_some());

    assert!(ptr::eq(
        bytes.metadata::<Metadata>().unwrap(),
        clone.metadata::<Metadata>().unwrap()
    ));

    assert!(!metadata.dropped.load(Ordering::Relaxed));
    drop(bytes);
    drop(clone);
    assert!(metadata.dropped.load(Ordering::Relaxed));
}

// #[test]
// fn unit_metadata() {
//     let bytes = <ArcBytes>::new_static(&[]);
//     assert!(ptr::eq(
//         bytes.metadata::<()>().unwrap(),
//         bytes.clone().metadata::<()>().unwrap()
//     ));
//     let bytes = <ArcBytes>::new(vec![]);
//     assert!(ptr::eq(
//         bytes.metadata::<()>().unwrap(),
//         bytes.clone().metadata::<()>().unwrap()
//     ));
// }

// // buffer cannot be downcast if there are clones or if it is a subslice
// #[test]
// fn downcast_buffer() {
//     let array = [0u8, 1, 2, 3];
//     let bytes = <ArcBytes>::new(array);
//     assert_eq!(bytes.try_into_buffer::<[u8; 4]>().unwrap(), [0, 1, 2, 3]);
//
//     let bytes = <ArcBytes>::new(array);
//     let clone = bytes.clone();
//     assert!(bytes.try_into_buffer::<[u8; 4]>().is_err());
//     assert_eq!(clone.try_into_buffer::<[u8; 4]>().unwrap(), [0, 1, 2, 3]);
//
//     let mut bytes = <ArcBytes>::new(array);
//     bytes.truncate(2);
//     assert!(bytes.try_into_buffer::<[u8; 4]>().is_err());
//
//     let mut bytes = <ArcBytes>::new(array);
//     bytes.advance(2);
//     assert!(bytes.try_into_buffer::<[u8; 4]>().is_err());
// }
//
// // vec cannot be downcast if there are clones, but it works with subslices
// #[test]
// fn downcast_vec() {
//     let bytes = <ArcBytes>::new(vec![42]);
//     assert_eq!(bytes.try_into_buffer::<Vec<u8>>().unwrap(), [42]);
//
//     let bytes = <ArcBytes>::new(vec![42]);
//     let clone = bytes.clone();
//     assert!(bytes.try_into_buffer::<Vec<u8>>().is_err());
//     assert_eq!(clone.try_into_buffer::<Vec<u8>>().unwrap(), [42]);
//
//     let mut bytes = <ArcBytes>::new(vec![0, 1, 2, 3]);
//     bytes.truncate(2);
//     assert_eq!(bytes.try_into_buffer::<Vec<u8>>().unwrap(), [0, 1]);
//
//     let mut bytes = <ArcBytes>::new(vec![0, 1, 2, 3]);
//     bytes.advance(2);
//     assert_eq!(bytes.try_into_buffer::<Vec<u8>>().unwrap(), [2, 3]);
// }
//
// // static slices can always be downcast
// #[test]
// fn downcast_static() {
//     let bytes = <ArcBytes>::new_static(&[0, 1, 2, 3]);
//     let subslice = bytes.subslice(..2);
//     assert_eq!(subslice.try_into_buffer::<&'static [u8]>().unwrap(), [0, 1]);
//     assert_eq!(
//         bytes.try_into_buffer::<&'static [u8]>().unwrap(),
//         [0, 1, 2, 3]
//     );
// }
//
// // `with_metadata` with unit metadata is like `new`, so a static subslice can be downcast
// // it would not be the case if unit metadata was not handled specially
// #[test]
// fn downcast_static_with_unit_metadata() {
//     let bytes = <ArcBytes>::from_buffer_with_metadata(<&'static [u8]>::from(&[0, 1, 2, 3]), ());
//     let subslice = bytes.subslice(..2);
//     assert_eq!(subslice.try_into_buffer::<&'static [u8]>().unwrap(), [0, 1]);
// }
//
// // ensure the metadata is dropped when the slice is downcast
// #[test]
// fn downcast_buffer_with_metadata() {
//     let metadata = Metadata::default();
//     let bytes = <ArcBytes>::from_buffer_with_metadata(vec![42], metadata.clone());
//     let _ = bytes.try_into_buffer::<Vec<u8>>().unwrap();
//     assert!(metadata.dropped.load(Ordering::Relaxed));
// }
//
// #[test]
// fn try_into_mut() {
//     let bytes = <ArcBytes>::new(vec![42]);
//     bytes.try_into_mut().unwrap();
// }
//
// #[test]
// fn inlined() {
//     let mut bytes = <ArcBytes>::new([0, 1, 2, 3]);
//     assert_eq!(bytes, [0, 1, 2, 3]);
//     assert_eq!(bytes.split_off(2), [2, 3]);
//     assert_eq!(bytes, [0, 1]);
// }