问题描述
是否有可能使用mappend /条件类型来转换此DU
type MyDU =
| {kind: 'foo'}
| {kind: 'bar'}
type Transformed = DUTransformer<MyDU>
这样我们就可以得到以下结果
type Transformed =
| {kind: 'foo',foo: boolean}
| {kind: 'bar',bar: boolean}
解决方法
是的,因为TypeScript将distribute mapped types over a union:
type MyDU =
| {kind: 'foo'}
| {kind: 'bar'}
type Kinded<T extends string> = { kind: T }
type DUTransformer<T> = T extends Kinded<infer K> ? T & {[K1 in K]: boolean} : never
type Transformed = DUTransformer<MyDU>
Transformed
的类型是:
type Transformed = ({
kind: 'foo';
} & {
foo: boolean;
}) | ({
kind: 'bar';
} & {
bar: boolean;
})