Minor: Clarify NullBufferBuilder::new capacity parameter (#7016)

* Minor: Clarify NullBufferBuilder::new capacity parameter * Update arrow-buffer/src/builder/null.rs Co-authored-by: Jeffrey Vo <[email protected]> --------- Co-authored-by: Jeffrey Vo <[email protected]>
apache · Jan 25, 2025 · 6340d46 · 6340d46
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commit 6340d46
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Showing 2 changed files with 9 additions and 2 deletions.
diff --git a/arrow-buffer/src/builder/boolean.rs b/arrow-buffer/src/builder/boolean.rs
@@ -32,7 +32,11 @@ pub struct BooleanBufferBuilder {
 }
 
 impl BooleanBufferBuilder {
-    /// Creates a new `BooleanBufferBuilder`
+    /// Creates a new `BooleanBufferBuilder` with sufficient space for
+    /// `capacity` bits (not bytes).
+    ///
+    /// The capacity is rounded up to the nearest multiple of 8 for the
+    /// allocation.
     #[inline]
     pub fn new(capacity: usize) -> Self {
         let byte_capacity = bit_util::ceil(capacity, 8);

diff --git a/arrow-buffer/src/builder/null.rs b/arrow-buffer/src/builder/null.rs
@@ -54,7 +54,10 @@ pub struct NullBufferBuilder {
 
 impl NullBufferBuilder {
     /// Creates a new empty builder.
-    /// `capacity` is the number of bits in the null buffer.
+    ///
+    /// Note that this method does not allocate any memory, regardless of the
+    /// `capacity` parameter. If an allocation is required, `capacity` is the
+    /// size in bits (not bytes) that will be allocated at minimum.
     pub fn new(capacity: usize) -> Self {
         Self {
             bitmap_builder: None,