ah, sorry again for being so slow on the uptake. ( I am being lazy and not reading all of the code ;) )

The list of all tracks in the generator ends up being a nasty bit of global state.

As long as you don't change the external behavior of `link` and the results when the 'standard' classes are passed in (which I _hope_ the existing tests ensure) don't be too shy about modifying the guts.

It might also be worth looking at how @nkeim does this in his interface. Another project I want to do is to get his fork merged back in with the ability to choose the linking backend at run time.  His to be fast, this one so you don't have to install numba) so unifying the interfaces would be good.