This is a small demonstration of a technique for emulating Higher-Kinded Types (HKTs)/Generalised Associated Types(GATs) through existing language features.
Basically, you can emulate T::F<X> as being <T::F as Plug<X>>::result_t with the Plug trait, and you can destructure F<X> down to F<_>, A through the Unplug trait.
You can read more about how this works with the original post and the followup.