This is also one of my favorites, but it can get even more verbose. However this is how the go type system is designed to work with covariance. Without the `~` operator these functions could only be used for a much smaller range of inputs.

But this complexity is an implementation detail of the library, you do not have to understand it as a user of these functions. From my perspective it is a valid approach to move complexity from use application layer into the library layer, so it can be hidden there and tested once.