viirya commented on code in PR #7911:
URL: https://github.com/apache/arrow-rs/pull/7911#discussion_r2223455775
##########
parquet-variant-compute/src/variant_array_builder.rs:
##########
@@ -168,7 +174,171 @@ impl VariantArrayBuilder {
self.value_buffer.extend_from_slice(value);
}
- // TODO: Return a Variant builder that will write to the underlying
buffers (TODO)
+ /// Return a `VariantArrayVariantBuilder` that writes directly to the
+ /// buffers of this builder.
+ ///
+ /// You must call [`VariantArrayVariantBuilder::finish`] to complete the
builder
+ ///
+ /// # Example
+ /// ```
+ /// # use parquet_variant::{Variant, VariantBuilder, VariantBuilderExt};
+ /// # use parquet_variant_compute::{VariantArray, VariantArrayBuilder};
+ /// let mut array_builder = VariantArrayBuilder::new(10);
+ ///
+ /// // First row has a string
+ /// let mut variant_builder = array_builder.variant_builder();
+ /// variant_builder.append_value("Hello, World!");
+ /// // must call finish to write the variant to the buffers
+ /// variant_builder.finish();
+ ///
+ /// // Second row is an object
+ /// let mut variant_builder = array_builder.variant_builder();
+ /// variant_builder
+ /// .new_object()
+ /// .with_field("my_field", 42i64)
+ /// .finish()
+ /// .unwrap();
+ /// variant_builder.finish();
+ ///
+ /// // finalize the array
+ /// let variant_array: VariantArray = array_builder.build();
+ ///
+ /// // verify what we wrote is still there
+ /// assert_eq!(variant_array.value(0), Variant::from("Hello, World!"));
+ /// assert!(variant_array.value(1).as_object().is_some());
+ /// ```
+ pub fn variant_builder(&mut self) -> VariantArrayVariantBuilder {
+ // append directly into the metadata and value buffers
+ let metadata_buffer = std::mem::take(&mut self.metadata_buffer);
+ let value_buffer = std::mem::take(&mut self.value_buffer);
+ VariantArrayVariantBuilder::new(self, metadata_buffer, value_buffer)
+ }
+}
+
+/// A `VariantBuilder` that writes directly to the buffers of a
`VariantArrayBuilder`.
+///
+/// Note this struct implements [`VariantBuilderExt`], so it can be used
+/// as a drop-in replacement for [`VariantBuilder`] in most cases.
Review Comment:
```suggestion
// This struct implements [`VariantBuilderExt`], so in most cases it can be
used as a
// [`VariantBuilder`] to perform variant-related operations for
[`VariantArrayBuilder`].
```
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