datafusion-expr 27.0.0

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//
//   http://www.apache.org/licenses/LICENSE-2.0
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use arrow::datatypes::DataType;

use super::binary::comparison_coercion;

/// Attempts to coerce the types of `list_types` to be comparable with the
/// `expr_type`.
/// Returns the common data type for `expr_type` and `list_types`
pub fn get_coerce_type_for_list(
    expr_type: &DataType,
    list_types: &[DataType],
) -> Option<DataType> {
    list_types
        .iter()
        .fold(Some(expr_type.clone()), |left, right_type| match left {
            None => None,
            Some(left_type) => comparison_coercion(&left_type, right_type),
        })
}

/// Find a common coerceable type for all `when_or_then_types` as well
/// and the `case_or_else_type`, if specified.
/// Returns the common data type for `when_or_then_types` and `case_or_else_type`
pub fn get_coerce_type_for_case_expression(
    when_or_then_types: &[DataType],
    case_or_else_type: Option<&DataType>,
) -> Option<DataType> {
    let case_or_else_type = match case_or_else_type {
        None => when_or_then_types[0].clone(),
        Some(data_type) => data_type.clone(),
    };
    when_or_then_types
        .iter()
        .fold(Some(case_or_else_type), |left, right_type| match left {
            // failed to find a valid coercion in a previous iteration
            None => None,
            // TODO: now just use the `equal` coercion rule for case when. If find the issue, and
            // refactor again.
            Some(left_type) => comparison_coercion(&left_type, right_type),
        })
}