[GitHub] [arrow-rs] alamb commented on a diff in pull request #3659: Implement std::fmt::Write for StringBuilder (#3638)

["alamb (via GitHub)" <gi...@apache.org>]

alamb commented on code in PR #3659:
URL: https://github.com/apache/arrow-rs/pull/3659#discussion_r1096582141


##########
arrow-array/src/builder/generic_bytes_builder.rs:
##########
@@ -235,6 +236,13 @@ impl<T: ByteArrayType, V: AsRef<T::Native>> Extend<Option<V>> for GenericByteBui
 ///  Array builder for [`GenericStringArray`][crate::GenericStringArray]
 pub type GenericStringBuilder<O> = GenericByteBuilder<GenericStringType<O>>;
 
+impl<O: OffsetSizeTrait> Write for GenericStringBuilder<O> {

Review Comment:
   ```suggestion
   /// Implement `Write` to support things like `write!(builder, ...`))
   ///
   /// Note each individual call to `write_str` will result in a new row in the builder
   impl<O: OffsetSizeTrait> Write for GenericStringBuilder<O> {
   ```



##########
arrow-array/src/builder/generic_bytes_builder.rs:
##########
@@ -443,4 +451,19 @@ mod tests {
         assert_eq!(array.value_offsets(), &[0, 1, 2, 3, 3, 4, 5, 6, 7, 15, 20]);
         assert_eq!(array.value_data(), b"abcabcdcupcakeshello");
     }
+
+    #[test]
+    fn test_write() {
+        let mut builder = GenericStringBuilder::<i32>::new();
+        write!(builder, "foo").unwrap();
+        builder.append_value("");
+        writeln!(builder, "bar").unwrap();
+        builder.append_value("");

Review Comment:
   This is quite neat 👍 



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