I think OP is claiming that if Swift had better meta programming abilities that GP have suggested, differentiable programming would have been a prime example for a good use of the capability.
If the language defines a way for you to ask the program for the computation graph in order to differentiate -- couldn't you add meta programming functions on top of that computation graph?
Seems to me like there's at least an argument that it should be possible grow diff programming into a general purpose meta programming system rather than use general purpose meta programming as implementation mechanism for differentiable programming ...
Seems to me like there's at least an argument that it should be possible grow diff programming into a general purpose meta programming system rather than use general purpose meta programming as implementation mechanism for differentiable programming ...