Nested

1import { readArray, readTupleNamed } from "./composite.js";
2import { type Reader } from "./core.js";
3
4/**
5 * `Nested(a T1, b T2, …)` has NO wire format of its own:
6 *  - `flatten_nested = 1` (the default): the column expands into separate
7 *    columns `a Array(T1)`, `b Array(T2)`, … — decode each with `readArray`.
8 *  - `flatten_nested = 0`: the column is `Array(Tuple(a T1, b T2, …))` — decode
9 *    with `readArray` + `readTupleNamed`.
10 *
11 * Either way it reuses existing readers; there is no dedicated Nested wire. This
12 * thin alias just composes the two for the `flatten_nested = 0` shape, as
13 * documentation that "Nested === Array(Tuple(...))":
14 *
15 *   readNested({ a: readUInt8, b: readString })
16 *     === readArray(readTupleNamed({ a: readUInt8, b: readString }))
17 *
18 * When generating code, prefer inlining (monomorphize the array + tuple) over
19 * this generic composition.
20 */
21export const readNested = <T extends Record<string, unknown>>(fields: {
22  [K in keyof T]: Reader<T[K]>;
23}): Reader<T[]> => readArray(readTupleNamed(fields));