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TS: KeysAssignableType
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| // copyright 2023 Zach Hardesty | |
| // TODO: check out https://www.totaltypescript.com/get-keys-of-an-object-where-values-are-of-a-given-type | |
| /** | |
| * Extracts keys of `TObj` that correspond to values that some type in the union | |
| * `TTypes` can be assigned to | |
| * | |
| * @template TObj Object to extract keys from | |
| * @template TTypes Type to check for assignability | |
| * @returns Union of keys of `TObj` that correspond to values that `TTypes` can be | |
| * assigned to | |
| */ | |
| type KeysAssignableType<TObj, TTypes> = { | |
| [P in keyof Required<TObj>]: TTypes extends Required<TObj>[P] ? P : never; | |
| }[keyof TObj]; | |
| type KeysAssignableExactType<TObj, TTypes> = { | |
| [P in keyof Required<TObj>]: [TTypes] extends [Required<TObj>[P]] ? P : never; | |
| }[keyof TObj]; | |
| interface ITestObj1 { | |
| a: string; | |
| b: number; | |
| c?: string; | |
| d?: number; | |
| e: boolean; | |
| f: string | number; | |
| g: undefined; | |
| h: null; | |
| i?: never; | |
| j: unknown; | |
| k: any; | |
| l: { a: string }; | |
| m: "a" | "b"; | |
| } | |
| type T0_0 = Expect<KeysAssignableType<ITestObj1, string>, "a" | "c" | "f" | "j" | "k">; | |
| type T1_0 = Expect< | |
| KeysAssignableType<ITestObj1, string | number>, | |
| "a" | "b" | "c" | "d" | "f" | "j" | "k" | |
| // REVIEW: more appropriate stricter type? | |
| // "f" | "j" | "k" | |
| >; | |
| type T2_0 = Expect<KeysAssignableType<ITestObj1, any>, keyof ITestObj1>; | |
| type T3_0 = Expect<KeysAssignableType<ITestObj1, object>, "j" | "k">; | |
| type T4_0 = Expect<KeysAssignableType<{}, any>, never>; | |
| type T5_0 = Expect< | |
| KeysAssignableType<ITestObj1, { a: string; b: number }>, | |
| "j" | "k" | "l" | |
| >; | |
| type T6_0 = Expect< | |
| KeysAssignableType<ITestObj1, "a">, | |
| "a" | "c" | "f" | "j" | "k" | "m" | |
| >; | |
| type T7_0 = Expect< | |
| KeysAssignableType<ITestObj1, "a" | "b" | "c">, | |
| "a" | "c" | "f" | "j" | "k" | "m" | |
| // REVIEW: more appropriate stricter type? | |
| // "a" | "c" | "f" | "j" | "k" | |
| >; | |
| type T8_0 = Expect< | |
| KeysAssignableType<ITestObj1, "a" | number>, | |
| "a" | "b" | "c" | "d" | "f" | "j" | "k" | "m" | |
| >; | |
| /** @see https://gist.github.com/zachhardesty7/1b5b6f6de328f1bb7c78cbe96ba5c720 */ | |
| type Expect< | |
| TInput extends TIntersect, | |
| TExpected extends TIntersect, | |
| TIntersect = TExpected & TInput, | |
| > = TInput; |
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