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Posted to github@arrow.apache.org by GitBox <gi...@apache.org> on 2022/06/13 20:22:44 UTC
[GitHub] [arrow-rs] alamb commented on a diff in pull request #1866: Mark typed buffer APIs safe (#996) (#1027)
alamb commented on code in PR #1866:
URL: https://github.com/apache/arrow-rs/pull/1866#discussion_r896100716
##########
arrow/src/buffer/immutable.rs:
##########
@@ -181,19 +181,14 @@ impl Buffer {
/// View buffer as typed slice.
///
- /// # Safety
+ /// # Panics
///
- /// `ArrowNativeType` is public so that it can be used as a trait bound for other public
- /// components, such as the `ToByteSlice` trait. However, this means that it can be
- /// implemented by user defined types, which it is not intended for.
- pub unsafe fn typed_data<T: ArrowNativeType + num::Num>(&self) -> &[T] {
- // JUSTIFICATION
- // Benefit
- // Many of the buffers represent specific types, and consumers of `Buffer` often need to re-interpret them.
- // Soundness
- // * The pointer is non-null by construction
- // * alignment asserted below.
- let (prefix, offsets, suffix) = self.as_slice().align_to::<T>();
+ /// This function panics if the underlying buffer is not aligned
+ /// correctly for type `T`.
+ pub fn typed_data<T: ArrowNativeType>(&self) -> &[T] {
+ // SAFETY
+ // ArrowNativeType are trivially transmutable, and this method checks alignment
Review Comment:
```suggestion
// ArrowNativeType is sealed (can't be implemented outside the arrow crate,
// trivially transmutable, and this method checks alignment
```
##########
arrow/src/buffer/immutable.rs:
##########
@@ -181,19 +181,14 @@ impl Buffer {
/// View buffer as typed slice.
///
- /// # Safety
+ /// # Panics
///
- /// `ArrowNativeType` is public so that it can be used as a trait bound for other public
- /// components, such as the `ToByteSlice` trait. However, this means that it can be
- /// implemented by user defined types, which it is not intended for.
- pub unsafe fn typed_data<T: ArrowNativeType + num::Num>(&self) -> &[T] {
- // JUSTIFICATION
- // Benefit
- // Many of the buffers represent specific types, and consumers of `Buffer` often need to re-interpret them.
- // Soundness
- // * The pointer is non-null by construction
- // * alignment asserted below.
- let (prefix, offsets, suffix) = self.as_slice().align_to::<T>();
+ /// This function panics if the underlying buffer is not aligned
+ /// correctly for type `T`.
+ pub fn typed_data<T: ArrowNativeType>(&self) -> &[T] {
Review Comment:
I wonder if this is truly "safe" -- is it really true that any bit pattern is a valid `ArrowNativeType`? I am thinking about floating point representations in particular -- I wonder if this API could potentially create invalid `f32` / `f64` which seems like it would thus still be `unsafe` 🤔
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