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remove MutableOpsBufferSupportedLhs and use unsafe mutable_buffer function #2

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remove MutableOpsBufferSupportedLhs and use unsafe mutable_buffer function #2

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78 changes: 26 additions & 52 deletions arrow-buffer/src/buffer/mutable_ops.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -52,41 +52,6 @@ impl BufferSupportedRhs for BooleanBufferBuilder {
}
}

/// Trait that will be operated on as the left-hand side (LHS) buffer in mutable operations.
///
/// This consumer of the trait must satisfies the following guarantees:
/// 1. It will not change the length of the buffer.
///
/// # Implementation notes
///
/// ## Why is this trait `pub(crate)`?
/// Because we don't wanna expose the inner mutable buffer to the public.
/// as this is the choice of the implementor of the trait and sometimes it is not desirable
/// (e.g. `BooleanBufferBuilder`).
///
/// ## Why this trait is needed, can't we just use `MutableBuffer` directly?
/// Sometimes we don't want to expose the inner `MutableBuffer`
/// so it can't be misused.
///
/// For example, [`BooleanBufferBuilder`] does not expose the inner `MutableBuffer`
/// as exposing it will allow the user to change the length of the buffer that will make the
/// `BooleanBufferBuilder` invalid.
///
pub(crate) trait MutableOpsBufferSupportedLhs {
/// Get a mutable reference to the inner `MutableBuffer`.
///
/// This is used to perform in-place operations on the buffer.
///
/// the caller must ensure that the length of the buffer is not changed.
fn inner_mutable_buffer(&mut self) -> &mut MutableBuffer;
}

impl MutableOpsBufferSupportedLhs for MutableBuffer {
fn inner_mutable_buffer(&mut self) -> &mut MutableBuffer {
self
}
}

/// Apply a binary bitwise operation to two bit-packed buffers.
///
/// This is the main entry point for binary operations. It handles both byte-aligned
Expand All @@ -106,7 +71,7 @@ impl MutableOpsBufferSupportedLhs for MutableBuffer {
reason = "MutableOpsBufferSupportedLhs and BufferSupportedRhs exposes the inner internals which is the implementor choice and we dont want to leak internals"
)]
pub fn mutable_bitwise_bin_op_helper<F>(
left: &mut impl MutableOpsBufferSupportedLhs,
left: &mut MutableBuffer,
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@alamb alamb Oct 24, 2025

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Rather than hiding what is going on with pub/hidden traits, I think it is clearer to simply pass in the MutableBuffer here

If you accept this PR and #1 we can avoid the #allow about private bounds as well

left_offset_in_bits: usize,
right: &impl BufferSupportedRhs,
right_offset_in_bits: usize,
Expand All @@ -119,7 +84,7 @@ pub fn mutable_bitwise_bin_op_helper<F>(
return;
}

let mutable_buffer = left.inner_mutable_buffer();
let mutable_buffer = left;

let mutable_buffer_len = mutable_buffer.len();
let mutable_buffer_cap = mutable_buffer.capacity();
Expand Down Expand Up @@ -734,7 +699,7 @@ fn handle_mutable_buffer_remainder_unary<F>(
reason = "MutableOpsBufferSupportedLhs exposes the inner internals which is the implementor choice and we dont want to leak internals"
)]
pub fn mutable_bitwise_unary_op_helper<F>(
buffer: &mut impl MutableOpsBufferSupportedLhs,
buffer: &mut MutableBuffer,
offset_in_bits: usize,
len_in_bits: usize,
mut op: F,
Expand All @@ -745,7 +710,7 @@ pub fn mutable_bitwise_unary_op_helper<F>(
return;
}

let mutable_buffer = buffer.inner_mutable_buffer();
let mutable_buffer = buffer;

let mutable_buffer_len = mutable_buffer.len();
let mutable_buffer_cap = mutable_buffer.capacity();
Expand Down Expand Up @@ -829,7 +794,7 @@ pub fn mutable_bitwise_unary_op_helper<F>(
reason = "MutableOpsBufferSupportedLhs and BufferSupportedRhs exposes the inner internals which is the implementor choice and we dont want to leak internals"
)]
pub fn mutable_buffer_bin_and(
left: &mut impl MutableOpsBufferSupportedLhs,
left: &mut MutableBuffer,
left_offset_in_bits: usize,
right: &impl BufferSupportedRhs,
right_offset_in_bits: usize,
Expand Down Expand Up @@ -863,7 +828,7 @@ pub fn mutable_buffer_bin_and(
reason = "MutableOpsBufferSupportedLhs and BufferSupportedRhs exposes the inner internals which is the implementor choice and we dont want to leak internals"
)]
pub fn mutable_buffer_bin_or(
left: &mut impl MutableOpsBufferSupportedLhs,
left: &mut MutableBuffer,
left_offset_in_bits: usize,
right: &impl BufferSupportedRhs,
right_offset_in_bits: usize,
Expand Down Expand Up @@ -897,7 +862,7 @@ pub fn mutable_buffer_bin_or(
reason = "MutableOpsBufferSupportedLhs and BufferSupportedRhs exposes the inner internals which is the implementor choice and we dont want to leak internals"
)]
pub fn mutable_buffer_bin_xor(
left: &mut impl MutableOpsBufferSupportedLhs,
left: &mut MutableBuffer,
left_offset_in_bits: usize,
right: &impl BufferSupportedRhs,
right_offset_in_bits: usize,
Expand Down Expand Up @@ -929,7 +894,7 @@ pub fn mutable_buffer_bin_xor(
reason = "MutableOpsBufferSupportedLhs exposes the inner internals which is the implementor choice and we dont want to leak internals"
)]
pub fn mutable_buffer_unary_not(
buffer: &mut impl MutableOpsBufferSupportedLhs,
buffer: &mut MutableBuffer,
offset_in_bits: usize,
len_in_bits: usize,
) {
Expand Down Expand Up @@ -964,14 +929,16 @@ mod tests {
.map(|(l, r)| expected_op(*l, *r))
.collect();

super::mutable_bitwise_bin_op_helper(
&mut left_buffer,
left_offset_in_bits,
right_buffer.inner(),
right_offset_in_bits,
len_in_bits,
op,
);
unsafe {
super::mutable_bitwise_bin_op_helper(
left_buffer.mutable_buffer(),
left_offset_in_bits,
right_buffer.inner(),
right_offset_in_bits,
len_in_bits,
op,
);
}

let result: Vec<bool> =
BitIterator::new(left_buffer.as_slice(), left_offset_in_bits, len_in_bits).collect();
Expand Down Expand Up @@ -1002,7 +969,14 @@ mod tests {
.map(|b| expected_op(*b))
.collect();

super::mutable_bitwise_unary_op_helper(&mut buffer, offset_in_bits, len_in_bits, op);
unsafe {
super::mutable_bitwise_unary_op_helper(
buffer.mutable_buffer(),
offset_in_bits,
len_in_bits,
op,
);
}

let result: Vec<bool> =
BitIterator::new(buffer.as_slice(), offset_in_bits, len_in_bits).collect();
Expand Down
16 changes: 9 additions & 7 deletions arrow-buffer/src/builder/boolean.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -16,9 +16,8 @@
// under the License.

use crate::{
BooleanBuffer, Buffer, MutableBuffer, MutableOpsBufferSupportedLhs, bit_mask, bit_util,
mutable_buffer_bin_and, mutable_buffer_bin_or, mutable_buffer_bin_xor,
mutable_buffer_unary_not,
BooleanBuffer, Buffer, MutableBuffer, bit_mask, bit_util, mutable_buffer_bin_and,
mutable_buffer_bin_or, mutable_buffer_bin_xor, mutable_buffer_unary_not,
};
use std::ops::{BitAnd, BitAndAssign, BitOr, BitOrAssign, BitXor, BitXorAssign, Not, Range};

Expand Down Expand Up @@ -260,11 +259,14 @@ impl BooleanBufferBuilder {
pub fn finish_cloned(&self) -> BooleanBuffer {
BooleanBuffer::new(Buffer::from_slice_ref(self.as_slice()), 0, self.len)
}
}

/// This trait is not public API so it does not leak the inner mutable buffer
impl MutableOpsBufferSupportedLhs for BooleanBufferBuilder {
fn inner_mutable_buffer(&mut self) -> &mut MutableBuffer {
/// Return a mutable reference to the internal buffer
///
/// # Safety
/// The caller must ensure that any modifications to the buffer maintain the invariant
/// `self.len < buffer.len() / 8` (that is that the buffer has enough capacity to hold `self.len` bits).
#[inline]
pub unsafe fn mutable_buffer(&mut self) -> &mut MutableBuffer {
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@alamb alamb Oct 24, 2025

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I personally think the code is much clearer and easier to understand if make a function that directly exposes the inner MutableBuffer (which is what the trait does) but mark it as unsafe, rather than relying on non public traits

&mut self.buffer
}
}
Expand Down