Function make_scalar_function

datafusion/functions/src/utils.rs:80–123

Creates a scalar function implementation for the given function. `inner` - the function to be executed `hints` - hints to be used when expanding scalars to arrays

(
    inner: F,
    hints: Vec<Hint>,
)

/// * `inner` - the function to be executed
/// * `hints` - hints to be used when expanding scalars to arrays
pub fn make_scalar_function<F>(
    inner: F,
    hints: Vec<Hint>,
) -> impl Fn(&[ColumnarValue]) -> Result<ColumnarValue>
where
    F: Fn(&[ArrayRef]) -> Result<ArrayRef>,
{
    move |args: &[ColumnarValue]| {
        // first, identify if any of the arguments is an Array. If yes, store its `len`,
        // as any scalar will need to be converted to an array of len `len`.
        let len = args
            .iter()
            .fold(Option::<usize>::None, |acc, arg| match arg {
                ColumnarValue::Scalar(_) => acc,
                ColumnarValue::Array(a) => Some(a.len()),
            });

        let is_scalar = len.is_none();

        let inferred_length = len.unwrap_or(1);
        let args = args
            .iter()
            .zip(hints.iter().chain(std::iter::repeat(&Hint::Pad)))
            .map(|(arg, hint)| {
                // Decide on the length to expand this scalar to depending
                // on the given hints.
                let expansion_len = match hint {
                    Hint::AcceptsSingular => 1,
                    Hint::Pad => inferred_length,
                };
                arg.to_array(expansion_len)
            })
            .collect::<Result<Vec<_>>>()?;

        let result = (inner)(&args);
        if is_scalar {
            // If all inputs are scalar, keeps output as scalar
            let result = result.and_then(|arr| ScalarValue::try_from_array(&arr, 0));
            result.map(ColumnarValue::Scalar)
        } else {
            result.map(ColumnarValue::Array)
        }
    }
}

/// Computes a binary math function for input arrays using a specified function.
/// Generic types: