What is TH? Why might you care? What is so horrible about it? What the heck is the generic/ folder? Why are we porting everything to C++? What are some downsides of having ported all our TH code to C++?

Further reading. 

• The TH to ATen porting guide has lots of explanations of old school TH idioms https://github.com/pytorch/pytorch/wiki/TH-to-ATen-porting-guide
• Old notes about refcounting in TH https://github.com/pytorch/pytorch/blob/master/aten/src/README.md