nominal types as enums

nominal-enum.ts

type Foo = 0 & { readonly brand?: unique symbol };
type Bar = 1 & { readonly brand?: unique symbol };
type Baz = 0 & { readonly brand?: unique symbol };

type Foobar = Foo | Bar;

const Foobar = {
    FOO: 0 as Foo,
    BAR: 1 as Bar,
};

const BAZ = 0 as Baz;

function foo(x: Foobar): number {
    return x;
}

foo(Foobar.FOO);
foo(Foobar.BAR);
foo(BAZ); // error