musli-zerocopy 0.0.65

use core::marker::PhantomData;

use crate::buf::MaybeUninit;
use crate::pointer::{DefaultSize, Size, Slice};
use crate::ZeroCopy;

/// A sized reference.
///
/// This is used to type a pointer with a [`ZeroCopy`] parameter so that it can
/// be used in combination with [`Buf`] to load the value from a buffer.
///
/// Note that the constructor is safe, because alignment and validation checks
/// happens whenever a value is loaded from a bare buffer.
///
/// [`Buf`]: crate::buf::Buf
///
/// # Examples
///
/// ```
/// use core::mem::align_of;
/// use musli_zerocopy::AlignedBuf;
/// use musli_zerocopy::pointer::Ref;
///
/// let mut buf = AlignedBuf::with_alignment::<u32>();
/// buf.extend_from_slice(&[1, 2, 3, 4]);
///
/// let buf = buf.as_ref();
///
/// let number = Ref::<u32>::new(0);
/// assert_eq!(*buf.load(number)?, u32::from_ne_bytes([1, 2, 3, 4]));
/// # Ok::<_, musli_zerocopy::Error>(())
/// ```
#[derive(Debug, ZeroCopy)]
#[repr(C)]
#[zero_copy(crate)]
pub struct Ref<T, O: Size = DefaultSize> {
    offset: O,
    #[zero_copy(ignore)]
    _marker: PhantomData<T>,
}

impl<T, O: Size> Ref<T, O> {
    // Construct a reference that does not require `T` to be `ZeroCopy`.
    pub(crate) fn new_raw(offset: usize) -> Self {
        let Some(offset) = O::from_usize(offset) else {
            panic!("Ref offset {offset} not in the legal range of 0-{}", O::MAX);
        };

        Self {
            offset,
            _marker: PhantomData,
        }
    }

    /// Get the offset the reference points to.
    ///
    /// # Examples
    ///
    /// ```
    /// use musli_zerocopy::pointer::Ref;
    ///
    /// let reference = Ref::<u64>::new(42);
    /// assert_eq!(reference.offset(), 42);
    /// ```
    #[inline]
    pub fn offset(&self) -> usize {
        self.offset.as_usize()
    }
}

impl<T, const N: usize, O: Size> Ref<[T; N], O>
where
    T: ZeroCopy,
{
    /// Coerce a reference to an array into a slice.
    ///
    /// # Examples
    ///
    /// ```
    /// use musli_zerocopy::AlignedBuf;
    ///
    /// let mut buf = AlignedBuf::new();
    ///
    /// let values = buf.store(&[1, 2, 3, 4]);
    /// let slice = values.into_slice();
    ///
    /// let buf = buf.as_aligned();
    ///
    /// assert_eq!(buf.load(slice)?, &[1, 2, 3, 4]);
    /// # Ok::<_, musli_zerocopy::Error>(())
    /// ```
    pub fn into_slice(self) -> Slice<T, O> {
        Slice::new_with_offset(self.offset, N)
    }
}

impl<T, O: Size> Ref<MaybeUninit<T>, O> {
    /// Assume that the reference is initialized.
    ///
    /// Unlike the counterpart in Rust, this isn't actually unsafe. Because in
    /// order to load the reference again we'd have to validate it anyways.
    #[inline]
    pub const fn assume_init(self) -> Ref<T, O> {
        Ref {
            offset: self.offset,
            _marker: PhantomData,
        }
    }
}

impl<T, O: Size> Ref<T, O>
where
    T: ZeroCopy,
{
    /// Construct a typed reference to the zeroeth offset in a buffer.
    ///
    /// # Examples
    ///
    /// ```
    /// use musli_zerocopy::pointer::Ref;
    ///
    /// let reference = Ref::<u64>::zero();
    /// assert_eq!(reference.offset(), 0);
    /// ```
    pub const fn zero() -> Self {
        Self {
            offset: O::ZERO,
            _marker: PhantomData,
        }
    }

    /// Construct a reference wrapping the given type at the specified offset.
    ///
    /// # Examples
    ///
    /// ```
    /// use musli_zerocopy::pointer::Ref;
    ///
    /// let reference = Ref::<u64>::new(42);
    /// assert_eq!(reference.offset(), 42);
    /// ```
    pub fn new(offset: usize) -> Self {
        Self::new_raw(offset)
    }
}

impl<T, O: Size> Clone for Ref<T, O> {
    #[inline]
    fn clone(&self) -> Self {
        *self
    }
}

impl<T, O: Size> Copy for Ref<T, O> {}