Implement CompactVector serialization

CHANGELOG.md

@@ -1,6 +1,7 @@
 # Changelog
 
 ## Unreleased
+- Added `CompactVector::to_bytes` and `from_bytes` for zero-copy serialization.
 - Made `DacsByte` generic over its flag index type with a default of `Rank9SelIndex`.
 - `DacsByte::from_slice` now accepts a generic index type, removing `from_slice_with_index`.
 - Added `BitVectorBuilder` and zero-copy `BitVectorData` backed by `anybytes::View`.

INVENTORY.md

@@ -9,6 +9,7 @@
 - Investigate alternative dense-select index strategies to replace removed `DArrayIndex`.
 - Explore additional index implementations leveraging the new generic `DacsByte<I>`.
 - Demonstrate the generic `from_slice` usage in examples and docs.
+- Show `CompactVector::to_bytes` and `from_bytes` in examples.
 
 ## Discovered Issues
 - `katex.html` performs manual string replacements; consider DOM-based manipulation.

README.md

@@ -29,6 +29,9 @@ is backed by `anybytes::View`. The data can be serialized with
 `BitVectorData::to_bytes` and reconstructed using `BitVectorData::from_bytes`,
 allowing zero-copy loading from an mmap or any other source by passing the
 byte region to `Bytes::from_source`.
+`CompactVector` offers similar helpers: `CompactVector::to_bytes` returns a
+metadata struct along with the raw bytes, and `CompactVector::from_bytes`
+reconstructs the vector from that information.
 
 ## Examples
 

src/int_vectors/compact_vector.rs

@@ -5,9 +5,10 @@ use anyhow::{anyhow, Result};
 use num_traits::ToPrimitive;
 
 use crate::bit_vector::BitVectorBuilder;
-use crate::bit_vector::{BitVector, NoIndex};
+use crate::bit_vector::{BitVector, BitVectorData, NoIndex};
 use crate::int_vectors::prelude::*;
 use crate::utils;
+use anybytes::Bytes;
 
 /// Mutable builder for [`CompactVector`].
 ///
@@ -184,6 +185,16 @@ impl Default for CompactVector {
     }
 }
 
+/// Metadata returned by [`CompactVector::to_bytes`] and required by
+/// [`CompactVector::from_bytes`].
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct CompactVectorMeta {
+    /// Number of integers stored.
+    pub len: usize,
+    /// Bit width for each integer.
+    pub width: usize,
+}
+
 impl CompactVector {
     /// Creates a new empty builder storing integers within `width` bits each.
     ///
@@ -411,6 +422,30 @@ impl CompactVector {
     pub const fn width(&self) -> usize {
         self.width
     }
+
+    /// Serializes the vector into a [`Bytes`] buffer and accompanying metadata.
+    pub fn to_bytes(&self) -> (CompactVectorMeta, Bytes) {
+        let (_, bytes) = self.chunks.data.to_bytes();
+        (
+            CompactVectorMeta {
+                len: self.len,
+                width: self.width,
+            },
+            bytes,
+        )
+    }
+
+    /// Reconstructs the vector from zero-copy [`Bytes`] and its metadata.
+    pub fn from_bytes(meta: CompactVectorMeta, bytes: Bytes) -> Result<Self> {
+        let data_len = meta.len * meta.width;
+        let data = BitVectorData::from_bytes(data_len, bytes)?;
+        let chunks = BitVector::new(data, NoIndex);
+        Ok(Self {
+            chunks,
+            len: meta.len,
+            width: meta.width,
+        })
+    }
 }
 
 impl Build for CompactVector {
@@ -656,4 +691,12 @@ mod tests {
         let cv = CompactVector::from_slice(&[1, 2, 3]).unwrap();
         assert_eq!(cv.to_vec(), vec![1, 2, 3]);
     }
+
+    #[test]
+    fn from_bytes_roundtrip() {
+        let cv = CompactVector::from_slice(&[4, 5, 6]).unwrap();
+        let (meta, bytes) = cv.to_bytes();
+        let other = CompactVector::from_bytes(meta, bytes).unwrap();
+        assert_eq!(cv, other);
+    }
 }