The article focusses on function overloads, which are not a part of Hindley-Milner (so yes, a red herring in this case) and not necessarily exponential. The fac

The article focusses on function overloads, which are not a part of Hindley-Milner (so yes, a red herring in this case) and not necessarily exponential. The fact that Swift is exponential here is an implementation shortcoming and little more. Swift's type checker does also have an exponential path for protocol constrained generic parameters which is functionally equivalent to the exponential path for classical Hindley-Milner. However, there are "pseudo" linear optimizations for this too that Swift should also consider.