[taharvey]

I suspect his comments are about the vision for the whole solution and environment, not just auto-diff, which is just a piece.

Auto-diff extends back 40 years. But the relative obscurity of its usage is that it is a "add-on", meta-programming step, or/and a limited sub-set of a language.

The Swift approach of 1st class compiler support is fairly unique. But also supports a future view of computing. If many problems can be solved by differentiable programming, not just the typical but somewhat niche NN/ML problems, then it needs to built into the whole language, not a sub-set.

But more importantly the future requirements, and death of Moore's Law means a fast, deeply statically analyzable language will be required to make the most of a heterogeneous computing environment.