[Requested Feature] Intersection types for enums

[Parasrah]

TypeScript Version: 2.6.1

Code

enum Fruit {
  APPLE = 'Apple',
}

enum Veggies {
  CARROT = 'Carrot',
}

type FruitAndVeggies
  = Fruit
  & Veggies;

Requested behavior:
An intersection type of Fruit & Veggies
ie the following:

type FruitAndVeggies = 'Apple' & 'Carrot';

Actual behavior:

type FruitAndVeggies = never

Use Case
Writing a Vue application with Typescript and using Vuex. I have used enums to enforce type strictness on the names of the mutations, actions and getters similar to the following:

export enum MutationTypes {
  SET_DRAWER_SHOWN = 'setDrawerShown',
}

const mutations = {
  [MutationTypes.SET_DRAWER_SHOWN] (state: AppState) {
    // ...
  },
};

Doing it this way however prevents me from using the Mutations = Module1Mutations | Module2Mutations type as an argument to commit mutations, if one of my <module>Mutations enums is empty (due to commit(type: string). I have created a workaround, but this feature would be nice if other people are also interested in it. Also if anyone has an appropriate solution that I haven't though of suggestions are welcome 😁

Thanks for Typescript!

[ghost]

'Apple' & 'Carrot' is indeed never because no string can be equal to 'Apple' but also be equal to 'Carrot'. Could you provide a simpler example of what you're trying to do?

[Parasrah]

Of course, having it explained that way makes my question seem dumb haha. Basically I have a situation like the following:

• 2 enums with string values
• A union type of both, which is essentially a union type of all the possible string values (correct me if I'm wrong)

The second that one of the enums is empty, the union type is no longer a union of strings, and therefore cannot be the parameter for a function requiring a string argument.

[ghost]

You can union string enums -- that uses the | type operator instead of &. But if an enum is empty we treat it as a number enum and not a string enum.

[Parasrah]

Alright, will just continue with the current workaround, thanks!