Enum ResolvedField 

enum ResolvedField {
    Single(Box<SingleFieldData>),
    ExpandedFixed(Box<ExpandedFixedData>),
    ExpandedVec(Box<ExpandedVecData>),
    AutoExpandVec(Box<AutoExpandVecData>),
    Struct(Box<StructFieldData>),
    Map(Box<MapFieldData>),
}

A resolved struct field ready for codegen – determines how this field maps to DataFrame companion struct columns.

Each variant represents a different expansion strategy:

• Single: one field -> one Vec<T> column
• ExpandedFixed: [T; N] -> N columns (name_1..name_N) at compile time
• ExpandedVec: Vec<T> + width = N -> N Vec<Option<T>> columns
• AutoExpandVec: Vec<T> + expand -> dynamic column count at runtime

Variants

Single(Box<SingleFieldData>)

Single column: name → Vec<ty>.

ExpandedFixed(Box<ExpandedFixedData>)

Expanded fixed array: name: [T; N] → name_1..name_N.

ExpandedVec(Box<ExpandedVecData>)

Expanded variable vec with pinned width: name: Vec<T> + width = N.

AutoExpandVec(Box<AutoExpandVecData>)

Auto-expanded Vec<T>/Box<[T]>: column count determined at runtime from max row length.

Struct(Box<StructFieldData>)

Struct field whose inner type implements DataFrameRow (issue #485). Companion holds Vec<Inner>; into_data_frame calls Inner::to_dataframe and flattens columns under the <base>_ prefix.

Map(Box<MapFieldData>)

Non-String-keyed HashMap<K,V> / BTreeMap<K,V> field (#919). Expands to two parallel list-columns <base>_keys / <base>_values, each a Vec<Vec<K>> / Vec<Vec<V>> (VECSXP of typed vectors). The reader zips keys[i] with values[i] back into the map type.

Layout

Note: Most layout information is completely unstable and may even differ between compilations. The only exception is types with certain repr(...) attributes. Please see the Rust Reference's “Type Layout” chapter for details on type layout guarantees.

Size: 16 bytes

Size for each variant:

• Single: 8 bytes
• ExpandedFixed: 8 bytes
• ExpandedVec: 8 bytes
• AutoExpandVec: 8 bytes
• Struct: 8 bytes
• Map: 8 bytes