Is there any way to get a specific member of a union type based on a key in the union without explicitly defining each member of the union?
type Thing = {
type: "person",
data: {
name: "John"
}
} | {
type: "building",
data: {
address: "111 Main Street"
}
}
type Person = Thing["where 'type' = 'person'"];
>Solution :
You can accomplish narrowing down via Distributive Conditional Types:
When conditional types act on a generic type, they become distributive when given a union type.
Then we use the fact that the union of type T and never is the same as T
type NarrowUnion<T, N> = T extends { type: N } ? T : never;
type Person = NarrowUnion<Thing, 'person'>