Mutable Keys

Implement the advanced util type MutableKeys, which picks all the mutable (not readonly) keys into a union.

For example:

type Keys = MutableKeys<{ readonly foo: string; bar: number }>;
// expected to be “bar”

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查看测试用例

import type { Equal, Expect } from '@type-challenges/utils'

type cases = [
  Expect<Equal<MutableKeys<{ a: number, readonly b: string }>, 'a'>>,
  Expect<Equal<MutableKeys<{ a: undefined, readonly b: undefined }>, 'a'>>,
  Expect<Equal<MutableKeys<{ a: undefined, readonly b?: undefined, c: string, d: null }>, 'a' | 'c' | 'd'>>,
  Expect<Equal<MutableKeys<{}>, never>>,
]