musli-zerocopy 0.0.51

use core::marker::PhantomData;

use crate::buf::{Buf, BufMut};
use crate::error::Error;
use crate::ptr::Ptr;
use crate::ZeroCopy;

/// A reference to a slice packed as a wide pointer.
///
/// This contains a pointer to the first element and the length of the slice.
///
/// # Examples
///
/// ```
/// use core::mem::align_of;
/// use musli_zerocopy::{OwnedBuf, Slice, Ptr};
///
/// let mut buf = OwnedBuf::with_alignment(align_of::<u32>());
/// buf.extend_from_slice(&[1, 2, 3, 4, 5, 6, 7, 8]);
///
/// let buf = buf.as_buf()?;
///
/// let slice = Slice::<u32>::new(Ptr::ZERO, 2);
///
/// let expected = [
///     u32::from_ne_bytes([1, 2, 3, 4]),
///     u32::from_ne_bytes([5, 6, 7, 8]),
/// ];
///
/// assert_eq!(buf.load(slice)?, &expected[..]);
/// # Ok::<_, musli_zerocopy::Error>(())
/// ```
///
/// Example using a slice with zero-sized elements:
///
/// ```
/// use core::mem::align_of;
/// use musli_zerocopy::{OwnedBuf, Slice, Ptr};
///
/// let buf = OwnedBuf::with_alignment(align_of::<()>());
/// let buf = buf.as_buf()?;
///
/// let slice = Slice::<()>::new(Ptr::ZERO, 2);
///
/// let expected = [(), ()];
///
/// assert_eq!(buf.load(slice)?, &expected[..]);
/// # Ok::<_, musli_zerocopy::Error>(())
/// ```
#[derive(Debug)]
#[repr(C)]
pub struct Slice<T: ?Sized> {
    ptr: Ptr,
    len: usize,
    _marker: PhantomData<T>,
}

impl<T: ?Sized> Slice<T> {
    /// Construct a new slice reference.
    ///
    /// # Examples
    ///
    /// ```
    /// use musli_zerocopy::{Slice, Ptr};
    ///
    /// let slice = Slice::<u32>::new(Ptr::ZERO, 2);
    /// # Ok::<_, musli_zerocopy::Error>(())
    /// ```
    pub fn new(ptr: Ptr, len: usize) -> Self {
        Self {
            ptr,
            len,
            _marker: PhantomData,
        }
    }

    /// The pointer part of the slice reference.
    ///
    /// # Examples
    ///
    /// ```
    /// use musli_zerocopy::{Slice, Ptr};
    ///
    /// let slice = Slice::<u32>::new(Ptr::ZERO, 2);
    /// assert_eq!(slice.ptr(), Ptr::ZERO);
    /// # Ok::<_, musli_zerocopy::Error>(())
    /// ```
    #[inline]
    pub fn ptr(&self) -> Ptr {
        self.ptr
    }

    /// The number of elements in the slice.
    ///
    /// # Examples
    ///
    /// ```
    /// use musli_zerocopy::{Slice, Ptr};
    ///
    /// let slice = Slice::<u32>::new(Ptr::ZERO, 2);
    /// assert_eq!(slice.len(), 2);
    /// # Ok::<_, musli_zerocopy::Error>(())
    /// ```
    #[inline]
    pub fn len(&self) -> usize {
        self.len
    }

    /// If the slice is empty.
    ///
    /// # Examples
    ///
    /// ```
    /// use musli_zerocopy::{Slice, Ptr};
    ///
    /// let slice = Slice::<u32>::new(Ptr::ZERO, 0);
    /// assert!(slice.is_empty());
    ///
    /// let slice = Slice::<u32>::new(Ptr::ZERO, 2);
    /// assert!(!slice.is_empty());
    /// # Ok::<_, musli_zerocopy::Error>(())
    /// ```
    pub fn is_empty(&self) -> bool {
        self.len == 0
    }
}

unsafe impl<T: ?Sized> ZeroCopy for Slice<T> {
    fn write_to<B: ?Sized>(&self, buf: &mut B) -> Result<(), Error>
    where
        B: BufMut,
    {
        buf.write(&self.ptr)?;
        buf.write(&self.len)?;
        Ok(())
    }

    fn read_from(buf: &Buf) -> Result<&Self, Error> {
        let mut v = buf.validate::<Self>()?;
        v.field::<Ptr>()?;
        v.field::<usize>()?;
        v.end()?;
        Ok(unsafe { buf.cast() })
    }

    unsafe fn validate_aligned(buf: &Buf) -> Result<(), Error> {
        let mut v = buf.validate_aligned()?;
        v.field::<Ptr>()?;
        v.field::<usize>()?;
        v.end()
    }
}

impl<T: ?Sized> Clone for Slice<T> {
    fn clone(&self) -> Self {
        *self
    }
}

impl<T: ?Sized> Copy for Slice<T> {}