struct utility

struct.ts

const s = {
  int64: <T extends string>(key: T) => [key, 8] as const,
  uint64: <T extends string>(key: T) => [key, 8] as const,
  float32: <T extends string>(key: T) => [key, 4] as const,
  float64: <T extends string>(key: T) => [key, 8] as const,
  int8: <T extends string>(key: T) => [key, 1] as const,
  int16: <T extends string>(key: T) => [key, 2] as const,
  int32: <T extends string>(key: T) => [key, 4] as const,
  uint8: <T extends string>(key: T) => [key, 1] as const,
  uint8clamped: <T extends string>(key: T) => [key, 1] as const,
  uint16: <T extends string>(key: T) => [key, 2] as const,
  uint32: <T extends string>(key: T) => [key, 4] as const,
} as const;

type Offsets = ReturnType<(typeof s)[keyof typeof s]>;

type Unique<T extends Offsets[]> = T extends [infer F, ...infer R]
  ? F extends Offsets
    ? R extends Offsets[]
      ? F[0] extends R[number][0]
        ? [never, ...Unique<R>]
        : [F, ...Unique<R>]
      : never
    : never
  : T;

function struct<T extends Offsets[]>(...scheme: Unique<T>) {
  let offset = 0;
  return Object.fromEntries(
    scheme.map(([key, value]) => {
      offset += value;
      return [key, offset];
    }),
  ) as Record<T[number][0], number>;
}

// Usage
const cons = struct(s.int32("cdr"), s.int32("car"));