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Implement std::fmt::Write for StringBuilder (#3638) #3659

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merged 2 commits into from
Feb 6, 2023
Merged

Implement std::fmt::Write for StringBuilder (#3638) #3659

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6bfa27b
Implement std::fmt::Write for StringBuilder (#3638)
tustvold Feb 4, 2023
44377ea
Add docs
tustvold Feb 6, 2023
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23 changes: 23 additions & 0 deletions arrow-array/src/builder/generic_bytes_builder.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -22,6 +22,7 @@ use crate::{ArrayRef, GenericByteArray, OffsetSizeTrait};
use arrow_buffer::{ArrowNativeType, Buffer, MutableBuffer};
use arrow_data::ArrayDataBuilder;
use std::any::Any;
use std::fmt::Write;
use std::sync::Arc;

/// Array builder for [`GenericByteArray`]
Expand Down Expand Up @@ -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> {
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Suggested change
impl<O: OffsetSizeTrait> Write for GenericStringBuilder<O> {
/// 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> {

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It might be weird if someone puts a BufWriter in front of the builder, but with some comments it should be ok

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Each individual call won't result in a new row, you need to explicitly append an empty string to delimit the record

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Excellent thing to document I think

fn write_str(&mut self, s: &str) -> std::fmt::Result {
self.value_builder.append_slice(s.as_bytes());
Ok(())
}
}

/// Array builder for [`GenericBinaryArray`][crate::GenericBinaryArray]
pub type GenericBinaryBuilder<O> = GenericByteBuilder<GenericBinaryType<O>>;

Expand Down Expand Up @@ -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("");
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This is quite neat 👍

write!(builder, "fiz").unwrap();
write!(builder, "buz").unwrap();
builder.append_value("");
let a = builder.finish();
let r: Vec<_> = a.iter().map(|x| x.unwrap()).collect();
assert_eq!(r, &["foo", "bar\n", "fizbuz"])
}
}