问题
I've the following tagged union interface
interface Example {
a: TypeA;
b: TypeB;
}
as an output I would like to convert this tagged union into an union type such as:
type oneOf<T> = ...
Where
var example: oneOf(Example); // would be { a: TypeA } | { b : TypeB }
I have not been able to map the type keys into an object having only the key as parameter. Any idea ?
回答1:
You can do it with a combination of:
- Distributive conditional types
- Mapped types
interface Example {
a: string;
b: number;
}
type SingleProperty<T, K extends keyof T> = K extends any ? {[Prop in K]: T[Prop]} : never
type UnionOfProperties<T> = { [K in keyof T]: SingleProperty<T, K> }[keyof T];
type ExamplePropertiesUnion = UnionOfProperties<Example>
This returns expected:
type ExamplePropertiesUnion = {
a: string;
} | {
b: number;
}
While the above is correct, TS will allow the following
var t: ExamplePropertiesUnion = {a: "", b: 42}
Which is NOT what we usually want:
Here below is the variant for a stricter type checking
type FixTsUnion<T, K extends keyof T> = {[Prop in keyof T]?: Prop extends K ? T[Prop]: never}
type oneOf<T> = { [K in keyof T]: Pick<T, K> & FixTsUnion<T, K>}[keyof T];
// ok
var z1: oneOf<Example> = { a: "" };
// ok
var z2: oneOf<Example> = { b: 5 };
// error
var z3: oneOf<Example> = { a: "", b: 34 };
// error
var z4: oneOf<Example> = { };
Try it here
See questions:
- TypeScript: Map union type to another union type
- Transform union type to intersection type
来源:https://stackoverflow.com/questions/62591230/typescript-convert-a-tagged-union-into-an-union-type