Make [MaybeUninit<T>] as Slab integration better

src/copy.rs

@@ -56,7 +56,7 @@ impl From<ComputedOffsets> for CopyRecord {
 /// things if you read the copied data in the wrong way. See the
 /// [crate-level Safety documentation][`crate#safety`] for more.
 #[inline(always)]
-pub fn copy_to_offset_exact<T: Copy, S: Slab>(
+pub fn copy_to_offset_exact<T: Copy, S: Slab + ?Sized>(
     src: &T,
     dst: &mut S,
     start_offset: usize,
@@ -84,7 +84,7 @@ pub fn copy_to_offset_exact<T: Copy, S: Slab>(
 /// things if you read the copied data in the wrong way. See the
 /// [crate-level Safety documentation][`crate#safety`] for more.
 #[inline(always)]
-pub fn copy_to_offset_with_align_exact<T: Copy, S: Slab>(
+pub fn copy_to_offset_with_align_exact<T: Copy, S: Slab + ?Sized>(
     src: &T,
     dst: &mut S,
     start_offset: usize,
@@ -127,7 +127,7 @@ pub fn copy_to_offset_with_align_exact<T: Copy, S: Slab>(
 /// things if you read the copied data in the wrong way. See the
 /// [crate-level Safety documentation][`crate#safety`] for more.
 #[inline]
-pub fn copy_to_offset<T: Copy, S: Slab>(
+pub fn copy_to_offset<T: Copy, S: Slab + ?Sized>(
     src: &T,
     dst: &mut S,
     start_offset: usize,
@@ -154,7 +154,7 @@ pub fn copy_to_offset<T: Copy, S: Slab>(
 /// things if you read the copied data in the wrong way. See the
 /// [crate-level Safety documentation][`crate#safety`] for more.
 #[inline]
-pub fn copy_to_offset_with_align<T: Copy, S: Slab>(
+pub fn copy_to_offset_with_align<T: Copy, S: Slab + ?Sized>(
     src: &T,
     dst: &mut S,
     start_offset: usize,
@@ -197,7 +197,7 @@ pub fn copy_to_offset_with_align<T: Copy, S: Slab>(
 /// things if you read the copied data in the wrong way. See the
 /// [crate-level Safety documentation][`crate#safety`] for more.
 #[inline]
-pub fn copy_from_slice_to_offset_exact<T: Copy, S: Slab>(
+pub fn copy_from_slice_to_offset_exact<T: Copy, S: Slab + ?Sized>(
     src: &[T],
     dst: &mut S,
     start_offset: usize,
@@ -225,7 +225,7 @@ pub fn copy_from_slice_to_offset_exact<T: Copy, S: Slab>(
 /// things if you read the copied data in the wrong way. See the
 /// [crate-level Safety documentation][`crate#safety`] for more.
 #[inline]
-pub fn copy_from_slice_to_offset_with_align_exact<T: Copy, S: Slab>(
+pub fn copy_from_slice_to_offset_with_align_exact<T: Copy, S: Slab + ?Sized>(
     src: &[T],
     dst: &mut S,
     start_offset: usize,
@@ -268,7 +268,7 @@ pub fn copy_from_slice_to_offset_with_align_exact<T: Copy, S: Slab>(
 /// things if you read the copied data in the wrong way. See the
 /// [crate-level Safety documentation][`crate#safety`] for more.
 #[inline]
-pub fn copy_from_slice_to_offset<T: Copy, S: Slab>(
+pub fn copy_from_slice_to_offset<T: Copy, S: Slab + ?Sized>(
     src: &[T],
     dst: &mut S,
     start_offset: usize,
@@ -297,7 +297,7 @@ pub fn copy_from_slice_to_offset<T: Copy, S: Slab>(
 /// things if you read the copied data in the wrong way. See the
 /// [crate-level Safety documentation][`crate#safety`] for more.
 #[inline]
-pub fn copy_from_slice_to_offset_with_align<T: Copy, S: Slab>(
+pub fn copy_from_slice_to_offset_with_align<T: Copy, S: Slab + ?Sized>(
     src: &[T],
     dst: &mut S,
     start_offset: usize,
@@ -351,7 +351,7 @@ pub fn copy_from_slice_to_offset_with_align<T: Copy, S: Slab>(
 /// [crate-level Safety documentation][`crate#safety`] for more.
 #[cfg(feature = "std")]
 #[inline]
-pub fn copy_from_iter_to_offset_with_align<T: Copy, Iter: Iterator<Item = T>, S: Slab>(
+pub fn copy_from_iter_to_offset_with_align<T: Copy, Iter: Iterator<Item = T>, S: Slab + ?Sized>(
     src: Iter,
     dst: &mut S,
     start_offset: usize,
@@ -374,7 +374,11 @@ pub fn copy_from_iter_to_offset_with_align<T: Copy, Iter: Iterator<Item = T>, S:
 /// Because of this, only one [`CopyRecord`] is returned specifying the record of the
 /// entire block of copied data. If the `src` iterator is empty, returns `None`.
 #[inline]
-pub fn copy_from_iter_to_offset_with_align_packed<T: Copy, Iter: Iterator<Item = T>, S: Slab>(
+pub fn copy_from_iter_to_offset_with_align_packed<
+    T: Copy,
+    Iter: Iterator<Item = T>,
+    S: Slab + ?Sized,
+>(
     mut src: Iter,
     dst: &mut S,
     start_offset: usize,
@@ -407,7 +411,7 @@ pub fn copy_from_iter_to_offset_with_align_packed<T: Copy, Iter: Iterator<Item =
 pub fn copy_from_iter_to_offset_with_align_exact_packed<
     T: Copy,
     Iter: Iterator<Item = T>,
-    S: Slab,
+    S: Slab + ?Sized,
 >(
     mut src: Iter,
     dst: &mut S,

src/lib.rs

@@ -360,10 +360,10 @@ pub unsafe trait Slab {
     }
 }
 
-// SAFETY: The captured `[MaybeUninit<u8>]` will all be part of the same allocation object, and borrowck
+// SAFETY: The captured `[MaybeUninit<T>]` will all be part of the same allocation object, and borrowck
 // will ensure that the borrows that occur on `self` on the relevant methods live long enough since they are
 // native borrows anyway.
-unsafe impl Slab for [MaybeUninit<u8>] {
+unsafe impl<T> Slab for [MaybeUninit<T>] {
     fn base_ptr(&self) -> *const u8 {
         self.as_ptr().cast()
     }
@@ -611,7 +611,7 @@ pub(crate) struct ComputedOffsets {
 
 /// Compute and validate offsets for a copy or read operation with the given parameters.
 #[inline(always)]
-pub(crate) fn compute_and_validate_offsets<S: Slab>(
+pub(crate) fn compute_and_validate_offsets<S: Slab + ?Sized>(
     slab: &S,
     start_offset: usize,
     t_layout: Layout,
@@ -662,10 +662,11 @@ fn align_offset_up_to(ptr: usize, offset: usize, align: usize) -> Option<usize>
     Some(aligned_ptr - ptr)
 }
 
-/// Make a `[MaybeUninit<u8>; N]` on the stack, which implements [`Slab`] and can therefore be used
+/// Make a `[MaybeUninit<T>; N]` on the stack, which implements [`Slab`] and can therefore be used
 /// with many of the helpers provided by this crate.
-pub fn make_stack_slab<const N: usize>() -> [MaybeUninit<u8>; N] {
-    [MaybeUninit::uninit(); N]
+pub fn make_stack_slab<T, const N: usize>() -> [MaybeUninit<T>; N] {
+    // SAFETY: An uninitialized `[MaybeUninit<_>; N]` is valid.
+    unsafe { MaybeUninit::<[MaybeUninit<T>; N]>::uninit().assume_init() }
 }
 
 /// A raw allocation on the heap which implements [`Slab`] and gets deallocated on [`Drop`].
@@ -721,3 +722,62 @@ unsafe impl Slab for HeapSlab {
         self.layout.size()
     }
 }
+
+#[cfg(test)]
+mod test {
+    use core::ffi::c_void;
+    use core::ptr::NonNull;
+
+    use crate::copy_from_slice_to_offset;
+    use crate::make_stack_slab;
+    use crate::readback_slice_from_ffi;
+    use crate::RawAllocation;
+
+    #[test]
+    fn readback_ffi() {
+        #[repr(C)]
+        #[derive(Clone, Copy, Default, PartialEq, Debug)]
+        struct OverlapHit {
+            pos: [f32; 3],
+            normal: [f32; 3],
+        }
+
+        const MAX_HITS: usize = 32;
+
+        let mut hits_slab = make_stack_slab::<OverlapHit, MAX_HITS>();
+
+        let readback_hits = unsafe {
+            readback_slice_from_ffi(hits_slab.as_mut_slice(), |ptr, _| {
+                let written_hits = ffi_get_hits(ptr, MAX_HITS);
+                written_hits
+            })
+        }
+        .unwrap();
+
+        assert_eq!(&HITS_TO_WRITE, readback_hits);
+
+        const HITS_TO_WRITE: [OverlapHit; 2] = [
+            OverlapHit {
+                pos: [1.0, 2.0, 10.0],
+                normal: [0.0, 1.0, 0.0],
+            },
+            OverlapHit {
+                pos: [11.0, 5.0, 100.0],
+                normal: [0.0, 0.0, 1.0],
+            },
+        ];
+
+        // simulate C ffi call to a physics lib
+        fn ffi_get_hits(out_hits: *mut c_void, max_len: usize) -> usize {
+            let mut slab = RawAllocation {
+                base_ptr: NonNull::new(out_hits.cast()).unwrap(),
+                size: max_len * core::mem::size_of::<OverlapHit>(),
+            };
+
+            copy_from_slice_to_offset(&HITS_TO_WRITE, &mut unsafe { slab.borrow_as_slab() }, 0)
+                .unwrap();
+
+            return HITS_TO_WRITE.len();
+        }
+    }
+}

src/read.rs

@@ -22,7 +22,7 @@ use super::*;
 /// See [this rust reference page](https://doc.rust-lang.org/reference/behavior-considered-undefined.html) for more details.
 pub unsafe fn readback_from_ffi<'a, T, S, F>(slab: &'a mut S, fill_slab: F) -> Result<&'a T, Error>
 where
-    S: Slab,
+    S: Slab + ?Sized,
     F: FnOnce(*mut c_void),
 {
     let t_layout = Layout::new::<T>();
@@ -68,7 +68,7 @@ pub unsafe fn readback_slice_from_ffi<'a, T, S, F>(
     fill_slab: F,
 ) -> Result<&'a [T], Error>
 where
-    S: Slab,
+    S: Slab + ?Sized,
     F: FnOnce(*mut c_void, usize) -> usize,
 {
     let t_layout = Layout::new::<T>();
@@ -112,7 +112,10 @@ where
 /// \* Validity is a complex topic not to be taken lightly.
 /// See [this rust reference page](https://doc.rust-lang.org/reference/behavior-considered-undefined.html) for more details.
 #[inline]
-pub unsafe fn read_at_offset<'a, T, S: Slab>(slab: &'a S, offset: usize) -> Result<&'a T, Error> {
+pub unsafe fn read_at_offset<'a, T, S: Slab + ?Sized>(
+    slab: &'a S,
+    offset: usize,
+) -> Result<&'a T, Error> {
     let t_layout = Layout::new::<T>();
     let offsets = compute_and_validate_offsets(slab, offset, t_layout, 1, true)?;
 
@@ -144,7 +147,10 @@ pub unsafe fn read_at_offset<'a, T, S: Slab>(slab: &'a S, offset: usize) -> Resu
 /// \* Validity is a complex topic not to be taken lightly.
 /// See [this rust reference page](https://doc.rust-lang.org/reference/behavior-considered-undefined.html) for more details.
 #[inline]
-pub unsafe fn read_at_offset_unchecked<'a, T, S: Slab>(slab: &'a S, offset: usize) -> &'a T {
+pub unsafe fn read_at_offset_unchecked<'a, T, S: Slab + ?Sized>(
+    slab: &'a S,
+    offset: usize,
+) -> &'a T {
     // SAFETY: if offset is within the slab as guaranteed by function-level safety, this is
     // safe since a slab's size must be < isize::MAX
     let ptr = unsafe { slab.base_ptr().add(offset) }.cast::<T>();
@@ -182,7 +188,7 @@ pub unsafe fn read_at_offset_unchecked<'a, T, S: Slab>(slab: &'a S, offset: usiz
 /// \* Validity is a complex topic not to be taken lightly.
 /// See [this rust reference page](https://doc.rust-lang.org/reference/behavior-considered-undefined.html) for more details.
 #[inline]
-pub unsafe fn read_at_offset_mut<'a, T, S: Slab>(
+pub unsafe fn read_at_offset_mut<'a, T, S: Slab + ?Sized>(
     slab: &'a mut S,
     offset: usize,
 ) -> Result<&'a mut T, Error> {
@@ -225,7 +231,7 @@ pub unsafe fn read_at_offset_mut<'a, T, S: Slab>(
 /// \* Validity is a complex topic not to be taken lightly.
 /// See [this rust reference page](https://doc.rust-lang.org/reference/behavior-considered-undefined.html) for more details.
 #[inline]
-pub unsafe fn read_at_offset_mut_unchecked<'a, T, S: Slab>(
+pub unsafe fn read_at_offset_mut_unchecked<'a, T, S: Slab + ?Sized>(
     slab: &'a mut S,
     offset: usize,
 ) -> &'a mut T {
@@ -266,7 +272,7 @@ pub unsafe fn read_at_offset_mut_unchecked<'a, T, S: Slab>(
 /// \* Validity is a complex topic not to be taken lightly.
 /// See [this rust reference page](https://doc.rust-lang.org/reference/behavior-considered-undefined.html) for more details.
 #[inline]
-pub fn get_maybe_uninit_at_offset_mut<'a, T, S: Slab>(
+pub fn get_maybe_uninit_at_offset_mut<'a, T, S: Slab + ?Sized>(
     slab: &'a mut S,
     offset: usize,
 ) -> Result<&'a mut MaybeUninit<T>, Error> {
@@ -308,7 +314,7 @@ pub fn get_maybe_uninit_at_offset_mut<'a, T, S: Slab>(
 /// \* Validity is a complex topic not to be taken lightly.
 /// See [this rust reference page](https://doc.rust-lang.org/reference/behavior-considered-undefined.html) for more details.
 #[inline]
-pub unsafe fn get_maybe_uninit_at_offset_mut_unchecked<'a, T, S: Slab>(
+pub unsafe fn get_maybe_uninit_at_offset_mut_unchecked<'a, T, S: Slab + ?Sized>(
     slab: &'a mut S,
     offset: usize,
 ) -> &'a mut MaybeUninit<T> {
@@ -341,7 +347,7 @@ pub unsafe fn get_maybe_uninit_at_offset_mut_unchecked<'a, T, S: Slab>(
 /// \* Validity is a complex topic not to be taken lightly.
 /// See [this rust reference page](https://doc.rust-lang.org/reference/behavior-considered-undefined.html) for more details.
 #[inline]
-pub unsafe fn read_slice_at_offset<'a, T, S: Slab>(
+pub unsafe fn read_slice_at_offset<'a, T, S: Slab + ?Sized>(
     slab: &'a S,
     offset: usize,
     len: usize,
@@ -382,7 +388,7 @@ pub unsafe fn read_slice_at_offset<'a, T, S: Slab>(
 /// See [this rust reference page](https://doc.rust-lang.org/reference/behavior-considered-undefined.html) for more details.
 /// - See also safety docs of [`core::slice::from_raw_parts`].
 #[inline]
-pub unsafe fn read_slice_at_offset_unchecked<'a, T, S: Slab>(
+pub unsafe fn read_slice_at_offset_unchecked<'a, T, S: Slab + ?Sized>(
     slab: &'a S,
     offset: usize,
     len: usize,
@@ -425,7 +431,7 @@ pub unsafe fn read_slice_at_offset_unchecked<'a, T, S: Slab>(
 /// \* Validity is a complex topic not to be taken lightly.
 /// See [this rust reference page](https://doc.rust-lang.org/reference/behavior-considered-undefined.html) for more details.
 #[inline]
-pub unsafe fn read_slice_at_offset_mut<'a, T, S: Slab>(
+pub unsafe fn read_slice_at_offset_mut<'a, T, S: Slab + ?Sized>(
     slab: &'a mut S,
     offset: usize,
     len: usize,
@@ -474,7 +480,7 @@ pub unsafe fn read_slice_at_offset_mut<'a, T, S: Slab>(
 /// \* Validity is a complex topic not to be taken lightly.
 /// See [this rust reference page](https://doc.rust-lang.org/reference/behavior-considered-undefined.html) for more details.
 #[inline]
-pub unsafe fn read_slice_at_offset_mut_unchecked<'a, T, S: Slab>(
+pub unsafe fn read_slice_at_offset_mut_unchecked<'a, T, S: Slab + ?Sized>(
     slab: &'a mut S,
     offset: usize,
     len: usize,
@@ -517,7 +523,7 @@ pub unsafe fn read_slice_at_offset_mut_unchecked<'a, T, S: Slab>(
 /// \* Validity is a complex topic not to be taken lightly.
 /// See [this rust reference page](https://doc.rust-lang.org/reference/behavior-considered-undefined.html) for more details.
 #[inline]
-pub fn get_maybe_uninit_slice_at_offset_mut<'a, T, S: Slab>(
+pub fn get_maybe_uninit_slice_at_offset_mut<'a, T, S: Slab + ?Sized>(
     slab: &'a mut S,
     offset: usize,
     len: usize,
@@ -565,7 +571,7 @@ pub fn get_maybe_uninit_slice_at_offset_mut<'a, T, S: Slab>(
 /// \* Validity is a complex topic not to be taken lightly.
 /// See [this rust reference page](https://doc.rust-lang.org/reference/behavior-considered-undefined.html) for more details.
 #[inline]
-pub unsafe fn get_maybe_uninit_slice_at_offset_mut_unchecked<'a, T, S: Slab>(
+pub unsafe fn get_maybe_uninit_slice_at_offset_mut_unchecked<'a, T, S: Slab + ?Sized>(
     slab: &'a mut S,
     offset: usize,
     len: usize,