DeepPartial 및 DeepReadonly

깊은 유틸리티 타입이 필요한 이유

interface Config {
  db: { host: string; port: number };
  app: { name: string };
}
type Shallow = Partial<Config>;
// Shallow.db is still required — only top level is optional

DeepPartial 구현하기

type DeepPartial<T> = T extends object
  ? { [K in keyof T]?: DeepPartial<T[K]> }
  : T;

DeepPartial 실제 사용

type PartialConfig = DeepPartial<Config>;
// PartialConfig.db?: { host?: string; port?: number }

const c: PartialConfig = { db: { host: "localhost" } };
// No error — all other fields are optional

DeepReadonly 구현하기

type DeepReadonly<T> = T extends object
  ? { readonly [K in keyof T]: DeepReadonly<T[K]> }
  : T;

DeepReadonly 실제 사용

type ReadonlyConfig = DeepReadonly<Config>;
const cfg: ReadonlyConfig = { db: { host: "localhost", port: 5432 }, app: { name: "my-app" } };
// cfg.db.port = 3000; // Error: readonly

깊은 타입에서 배열 처리하기

type DeepPartial<T> =
  T extends (infer U)[]
    ? DeepPartial<U>[]
    : T extends object
      ? { [K in keyof T]?: DeepPartial<T[K]> }
      : T;

원시 타입 처리하기

type DeepReadonly<T> =
  T extends string | number | boolean | null | undefined ? T
  : T extends (infer U)[] ? ReadonlyArray<DeepReadonly<U>>
  : { readonly [K in keyof T]: DeepReadonly<T[K]> };

DeepPartial과 DeepReadonly 결합하기

type SafePatch<T> = DeepReadonly<DeepPartial<T>>;

성능 고려 사항

// For very deep schemas, consider using Zod or io-ts
// which provide runtime + compile-time deep typing

실제 사용: React 상태 패치

function patch<T>(state: T, changes: DeepPartial<T>): T {
  return { ...state, ...changes } as T;
}

요약: 깊은 유틸리티 타입

빠른 확인

학습 내용