[Typescript] 122. Hard - 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”
/* _____________ Your Code Here _____________ */
type MutableKeys<T> = keyof {
[Key in keyof T as Equal<Pick<T, Key>, Readonly<Pick<T, Key>>> extends true ? never: Key]: T[Key]
}
/* _____________ Test Cases _____________ */
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>>,
]
分类:
TypeScript
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