rocket-auth-login VS case-studies

There is https://github.com/vishusandy/rocket-auth-login IIRC. It's "third-party" (e.g. not by the rocket team). I haven't used it really (just tinkered around with it). I am also no expert when it comes down to authentication. But I do remember taking a look at the code. It looked all right.

Luckily there is a workaround to emulate such a definition, which dtolnay discovered and explained here: https://github.com/dtolnay/case-studies/tree/b9802f6df8dc8e54970b83fb9af6df923b46abf5/unit-type-parameters.

I think they are talking about this one trick which the devs don't want you to know about. Note that while it looks like specialization, it works only in a few very limited cases and is quite fragile, so it's a hack, not a substitute for the real feature.

Also I suggest his case studies repo since you are looking at what is possible: https://github.com/dtolnay/case-studies

/u/dtolnay has a great case studies repository.

Once you have the basics down, read dtolnay's case studies. They show how to do advanced stuff with easy macros.

You can use "Autoref-based stable specialization" or use/mimic the impls crate.

With a subset of specialization likely riding the trains soon and a workaround available, why would you give up?

Addendum: Technically there are various hacks out in the wild that can get something like this working using macros, but their usefulness is more limited. Once generics are in play, they stop working for the same reason and you are back to square one. Such approaches include autoref specialization which (ab)uses type inferrence to select different methods with the same name (kind of similar to what you seemed to be trying to do) and OIBIT specialization, which relies on a different nightly feature.

this works since values and types are in different namespaces (see: Rusts Universes or dtolnay's Case Study about "Unit struct with type parameters")

To do this with traits you would need specialization but since you are using macros you should be able to use "Autoref-based stable specialization". Here is a playground which uses the latter approach to implement the wanted macro without using any nightly features.