Differentiable programming for gradient-based machine learning

[dan-zheng]

@rxwei

It seems to me that the only reason such protocols exist is because type alias declarations don't support where clauses. I don't believe that we should introduce an additional protocol for this purpose.

Yep, adding an extra protocol is certainly not as ideal.

About typealiases with generic requirements: check out this thread. Seems like the feature could be implemented with a moderate amount of compiler hacking.