Enum FieldTypeKind 

pub(crate) enum FieldTypeKind<'a> {
    Scalar,
    FixedArray(&'a Type, usize),
    VariableVec(&'a Type),
    BoxedSlice(&'a Type),
    BorrowedSlice(&'a Type),
    Map {
        key_ty: &'a Type,
        val_ty: &'a Type,
    },
    Struct {
        inner_ty: &'a Type,
    },
}

Classification of a field type for DataFrame column expansion.

Used to decide whether a field maps to a single column or should be expanded into multiple suffixed columns (e.g., coords_1, coords_2).

Variants

Scalar

Single column (most types). No expansion.

FixedArray(&'a Type, usize)

[T; N] – fixed-size array, expands to N columns at compile time. Contains the element type and array length.

VariableVec(&'a Type)

Vec<T> – variable length, needs width attribute or expand for expansion. Contains the element type.

BoxedSlice(&'a Type)

Box<[T]> – owned slice, treated like Vec<T> for expansion purposes. Contains the element type.

BorrowedSlice(&'a Type)

&[T] – borrowed slice, treated like Vec<T> for expansion purposes. Contains the element type.

Map

HashMap<K, V> or BTreeMap<K, V>. The two derive paths treat maps differently:

• enum path: expands to two parallel list-columns <field>_keys / <field>_values (see enum_expansion.rs).
• struct path: resolves to a Single opaque list-of-named-lists column (Vec<map>: IntoR); reader-capable for String keys + reader-scalar values (#764, see SingleFieldData::map_reader).

Key order follows the map’s own iteration order: BTreeMap yields sorted keys, HashMap yields non-deterministic order.

Fields

key_ty: &'a Type

val_ty: &'a Type

Struct

A struct-typed field whose inner type implements DataFrameRow.

Flattened into <field>_<inner_col> prefixed columns by default. A compile-time assertion against ::miniextendr_api::markers::DataFrameRow is emitted so rustc gives a clear error when the inner type is missing the derive.

Suppressed by #[dataframe(as_list)] — with as_list the field becomes a Scalar and uses the ordinary single-column codegen path.

Fields

inner_ty: &'a Type

The full field type (used for the compile-time DataFrameRow assertion).

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: 24 bytes

Size for each variant:

• Scalar: 0 bytes
• FixedArray: 16 bytes
• VariableVec: 8 bytes
• BoxedSlice: 8 bytes
• BorrowedSlice: 8 bytes
• Map: 16 bytes
• Struct: 8 bytes