The Power of Discriminated Unions in TypeScript

Good question.

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Well, yes, you totally can, but the idea is not to have a `role` property. It is about differentiating between users during compilation and inferring which set of properties belong to a certain role. Having one huge type doesn't solve it.

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For instance, take the `Guest` type example. It doesn't have first, last name and email. `Admin` type on the contrary have all of them. It means you would have to make `firstName`, `lastName` and `email` optional when defining one big `User` type to satisfy **both** `Admin` and `Guest` constraints. In the end of the day `User` would be a large pile of optional properties without a clear semantic meaning.

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I hope this explanation makes sense.

Oleksandr Khrustalov