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Create matrix type from two discriminated unions

I have two discriminated unions in TypeScript:

type Person = "alice" | "bob"
type Number = 1 | 2

From these two discriminated unions, how can I create a new discriminated union from every possible combination:

type Desired = "alice-1" | "bob-1" | "alice-2" | "bob-2"

Ideally Desired is not hardcoded as Person and Number could get quite large. If needed, Number could be the string union "1" | "2".

Solution

  • You can just apply template literal types and you'll get the the desired type:

    type Person = "alice" | "bob"
type Number = 1 | 2

type Desired = `${Person}-${Number}`

    Playground Link

    This feature is available in Typescript since 4.1 with the addition of Template literal types and mapped type 'as' clauses