Question

Pick类型包含在TypeScript中。它的实现如下：

type Pick<T, K extends keyof T> = {
  [P in K]: T[P];
};

您将如何编写PickByValue类型，以使以下各项起作用：

type Test = {
  includeMe: 'a' as 'a',
  andMe: 'a' as 'a',
  butNotMe: 'b' as 'b',
  orMe: 'b' as 'b'
};

type IncludedKeys = keyof PickByValue<Test, 'a'>;
// IncludedKeys = 'includeMe' | 'andMe'

Answer 1

假设您打算Test成为这样：

type Test = {
  includeMe: 'a',
  andMe: 'a',
  butNotMe: 'b',
  orMe: 'b'
};

，并假设您希望PickByValue<T, V>给出V的子类型的所有属性（因此PickByValue<T, unknown>应该是T），则可以这样定义PickByValue：

type PickByValue<T, V> = Pick<T, { [K in keyof T]: T[K] extends V ? K : never }[keyof T]>
type TestA = PickByValue<Test, 'a'>; // {includeMe: "a"; andMe: "a"}
type IncludedKeys = keyof PickByValue<Test, 'a'>; // "includeMe" | "andMe"

但是，如果您只需要IncludedKeys，则可以使用KeysMatching<T, V>更直接地做到这一点：

type KeysMatching<T, V> = {[K in keyof T]: T[K] extends V ? K : never}[keyof T];
type IncludedKeysDirect = KeysMatching<Test, 'a'> // "includeMe" | "andMe"

希望有所帮助；祝你好运！

如何编写PickByValue类型？

1 个答案: