Struct StructFieldMapping 

pub struct StructFieldMapping {
    pub field_accessor: Arc<ScalarUDF>,
    pub fields: Vec<(Vec<ScalarValue>, usize)>,
}

Describes how a struct-producing UDF’s output fields correspond to its input arguments. This enables the optimizer to propagate orderings through struct projections (e.g., so that sorting by a struct field can be recognized as equivalent to sorting by the source column).

See ScalarUDFImpl::struct_field_mapping for details.

Fields

field_accessor: Arc<ScalarUDF>

The UDF used to construct field access expressions on the output. For example, the get_field UDF for accessing struct fields.

fields: Vec<(Vec<ScalarValue>, usize)>

For each output field: the literal arguments to pass to the field_accessor UDF (after the base expression), and the index of the corresponding input argument that produces the field’s value.

For named_struct('a', col1, 'b', col2), this would be: [(["a"], 1), (["b"], 3)] — field "a" comes from arg index 1.