Function write_leaf_to_string

datafusion/functions-nested/src/string.rs:752–781

Appends the string representation of each element in a leaf (non-list) array to `w`, separated by `delimiter`. Null elements are rendered using `null_string` if provided, or skipped otherwise. The `append` closure controls how each non-null element is written.

(
    w: &mut W,
    arr: &'a A,
    delimiter: &str,
    null_string: Option<&str>,
    first: &mut bool,
    append: impl Fn(&mut W, T) -> fmt::Result,
)

/// using `null_string` if provided, or skipped otherwise. The `append`
/// closure controls how each non-null element is written.
fn write_leaf_to_string<'a, W: Write, A, T>(
    w: &mut W,
    arr: &'a A,
    delimiter: &str,
    null_string: Option<&str>,
    first: &mut bool,
    append: impl Fn(&mut W, T) -> fmt::Result,
) -> Result<()>
where
    &'a A: IntoIterator<Item = Option<T>>,
{
    for x in arr {
        // Skip nulls when no null_string is provided
        if x.is_none() && null_string.is_none() {
            continue;
        }

        if *first {
            *first = false;
        } else {
            w.write_str(delimiter)?;
        }

        match x {
            Some(x) => append(w, x)?,
            None => w.write_str(null_string.unwrap())?,
        }
    }
    Ok(())
}

trait StringArrayBuilderType: ArrayBuilder {
    fn append_value(&mut self, val: &str);