fix(pick): return Partial<Pick<T, K>> for non-tuple key arrays

docs/ja/reference/object/pick.md

@@ -37,8 +37,11 @@ const picked = pick(nested, ['user', 'settings']);
 #### パラメータ
 
 - `obj` (`T extends Record<string, any>`): プロパティを選択するオブジェクトです。
-- `keys` (`readonly K[]`): オブジェクトから選択するキーの配列です。
+- `keys` (`readonly [...Keys]`): オブジェクトから選択するキーの配列またはタプルです。
 
 #### 戻り値
 
-(`Pick<T, K>`): 指定されたキーに対応するプロパティのみを含む新しいオブジェクトを返します。
+`keys`がタプルか可変長配列かによって、戻り値の型が変わります。
+
+- `keys`が**タプル**の場合（例: `['a', 'b']`）: `Pick<T, 'a' | 'b'>` を返します — 指定したキーがすべて存在することが保証されます。
+- `keys`が**可変長配列**の場合（例: `keys: ('a' | 'b')[]`）: `Partial<Pick<T, 'a' | 'b'>>` を返します — 配列に実際に含まれているキーのみが結果オブジェクトに存在します。

docs/ko/reference/object/pick.md

@@ -37,8 +37,11 @@ const picked = pick(nested, ['user', 'settings']);
 #### 파라미터
 
 - `obj` (`T extends Record<string, any>`): 속성들을 선택할 객체예요.
-- `keys` (`readonly K[]`): 객체에서 선택할 키들의 배열이에요.
+- `keys` (`readonly [...Keys]`): 객체에서 선택할 키들의 배열 또는 튜플이에요.
 
 #### 반환 값
 
-(`Pick<T, K>`): 지정된 키들에 해당하는 속성들만 포함한 새로운 객체를 반환해요.
+`keys`가 튜플인지 가변 길이 배열인지에 따라 반환 타입이 달라져요.
+
+- `keys`가 **튜플**인 경우 (예: `['a', 'b']`): `Pick<T, 'a' | 'b'>`를 반환해요 — 지정된 키들이 모두 존재하는 것이 보장돼요.
+- `keys`가 **가변 길이 배열**인 경우 (예: `keys: ('a' | 'b')[]`): `Partial<Pick<T, 'a' | 'b'>>`를 반환해요 — 배열에 실제로 포함된 키들만 결과 객체에 존재해요.

docs/reference/object/pick.md

@@ -37,8 +37,11 @@ const picked = pick(nested, ['user', 'settings']);
 #### Parameters
 
 - `obj` (`T extends Record<string, any>`): The object to select properties from.
-- `keys` (`readonly K[]`): An array of keys to select from the object.
+- `keys` (`readonly [...Keys]`): An array or tuple of keys to select from the object.
 
 #### Returns
 
-(`Pick<T, K>`): A new object containing only the properties corresponding to the specified keys.
+The return type depends on whether `keys` is a tuple or a variable-length array:
+
+- If `keys` is a **tuple** (e.g. `['a', 'b']`): returns `Pick<T, 'a' | 'b'>` — all specified keys are guaranteed to be present.
+- If `keys` is a **variable-length array** (e.g. `keys: ('a' | 'b')[]`): returns `Partial<Pick<T, 'a' | 'b'>>` — only the keys actually in the array will be present.

docs/zh_hans/reference/object/pick.md

@@ -37,8 +37,11 @@ const picked = pick(nested, ['user', 'settings']);
 #### 参数
 
 - `obj` (`T extends Record<string, any>`): 要选择属性的对象。
-- `keys` (`readonly K[]`): 要从对象中选择的键的数组。
+- `keys` (`readonly [...Keys]`): 要从对象中选择的键的数组或元组。
 
 #### 返回值
 
-(`Pick<T, K>`): 返回一个仅包含指定键对应属性的新对象。
+返回类型取决于 `keys` 是元组还是可变长度数组。
+
+- 如果 `keys` 是**元组**（例如 `['a', 'b']`）：返回 `Pick<T, 'a' | 'b'>` — 保证所有指定的键都存在。
+- 如果 `keys` 是**可变长度数组**（例如 `keys: ('a' | 'b')[]`）：返回 `Partial<Pick<T, 'a' | 'b'>>` — 只有数组中实际包含的键才会出现在结果对象中。

src/object/pick.spec.ts

@@ -1,4 +1,4 @@
-import { describe, expect, it } from 'vitest';
+import { describe, expect, expectTypeOf, it } from 'vitest';
 import { pick } from './pick';
 
 describe('pick', () => {
@@ -32,4 +32,19 @@ describe('pick', () => {
 
     expect(Reflect.ownKeys(result)).toEqual([]);
   });
+
+  it('should return Pick<T, K> when given a literal tuple (all keys guaranteed)', () => {
+    const obj = { a: 1, b: 2, c: 3 };
+    const result = pick(obj, ['a', 'b']);
+
+    expectTypeOf(result).toEqualTypeOf<Pick<typeof obj, 'a' | 'b'>>();
+  });
+
+  it('should return Partial<Pick<T, K>> when given a non-tuple array (not all keys guaranteed)', () => {
+    const obj = { a: 1, b: 2, c: 3 };
+    const keys: ('a' | 'b')[] = Math.random() > 0.5 ? ['a'] : ['b'];
+    const result = pick(obj, keys);
+
+    expectTypeOf(result).toEqualTypeOf<Partial<Pick<typeof obj, 'a' | 'b'>>>();
+  });
 });

src/object/pick.ts

@@ -4,19 +4,26 @@
  * This function takes an object and an array of keys, and returns a new object that
  * includes only the properties corresponding to the specified keys.
  *
+ * The return type depends on whether a tuple or a variable-length array is passed:
+ * - Tuple (e.g. `['a', 'b']`): returns `Pick<T, 'a' | 'b'>` — all keys are guaranteed present.
+ * - Array (e.g. `keys: ('a' | 'b')[]`): returns `Partial<Pick<T, 'a' | 'b'>>` — only some keys may be present.
+ *
  * @template T - The type of object.
- * @template K - The type of keys in object.
+ * @template Keys - The type of the keys array (tuple or array).
  * @param {T} obj - The object to pick keys from.
- * @param {K[]} keys - An array of keys to be picked from the object.
- * @returns {Pick<T, K>} A new object with the specified keys picked.
+ * @param {Keys} keys - An array of keys to be picked from the object.
+ * @returns A new object with the specified keys picked.
  *
  * @example
  * const obj = { a: 1, b: 2, c: 3 };
  * const result = pick(obj, ['a', 'c']);
  * // result will be { a: 1, c: 3 }
  */
-export function pick<T extends Record<string, any>, K extends keyof T>(obj: T, keys: readonly K[]): Pick<T, K> {
-  const result = {} as Pick<T, K>;
+export function pick<T extends Record<string, any>, Keys extends ReadonlyArray<keyof T>>(
+  obj: T,
+  keys: readonly [...Keys]
+): number extends Keys['length'] ? Partial<Pick<T, Keys[number]>> : Pick<T, Keys[number]> {
+  const result = {} as any;
 
   for (let i = 0; i < keys.length; i++) {
     const key = keys[i];