I don't love that example though, because the brand field's value of a string literal will make it seem like the object actually has a property named `__brand` when it doesn't. `never` is the best brand field type as far as I can tell.
`never` is a problematic field type, at least unless you make efforts (via non-exported symbols, for instance) to make sure the field is inaccessible - `never` is the type of a value that doesn't exist; it's there in the type system to signify an impossible scenario. For instance, a common use-case is to mark the type of a variable after type narrowing has exhausted every possible case.
If you assert that your id's actually do have a never-typed field, and you let your program access it, you're basically letting users enter an impossible state freely and easily.
Isn't that what you want to signify? It's the intent, and better than asserting that your IDs have a string-valued field that it doesn't.
Ideally you could brand with a private field, but we would probably need `typeof class` for that (assuming `typeof class` allows private members. I'm not sure).
From the direction of construction, it is - as a marker of "I want to never be able to construct this value - the only way I should be able to construct this value is in an impossible state", sure, it works.
But from the direction of usage...because you've used casting to (as far as TypeScript is concerned) construct the value, once it's floating around you're in an impossible state - and no, having a branded thing should not be an impossible state. Because of that you can freely violate the principles of the type system's logic - ex falso quodlibet.
A never value is effectively an any value, and now you have one on hand at all times.
The real problem with `never`, or at least the problem that could actually affect you in this scenario, is that it’s assignable to everything. Just like `any`, but even strict lint rules usually won’t catch the type safety it escapes.
If by some mistake your code gets a reference to a field with a `never` type, you’ll never get a type error passing or assigning that reference downstream. That’s relatively trivial to address if you can spot the (edit: runtime) errors it causes directly, but can wreak terrible havoc if it finds a path through several layers of function calls or whatever other indirection before the runtime consequences surface.
> Isn't that what you want to signify? It's the intent
No it isn't. If your ids do have a field, then marking them as never having a field is unwise. Never means that code that reads that field is never wrong (because you can never reach the point of reading it), whereas you want the opposite, code that reads that field is always wrong.
I don't love that example though, because the brand field's value of a string literal will make it seem like the object actually has a property named `__brand` when it doesn't. `never` is the best brand field type as far as I can tell.