The possibilty of specifying actions such as the creation of histograms without specifying the type of the column they act on is a killer feature. This is achieved getting the name of the type from the column, temporary or linked to a branch, and jitting the right code.
Jitting is per se blazing fast but presently there is an overhead in setting up the procedure.
The downside of type inference is therefore some less than optimal runtime performance due to the aforementioned overhead linked to jitting.
This could be solved deferring jitting, for example moving the actual jitting from the creation of the action to before the event loop, maybe in a single shot, packing together all the code. An analogous, but much more simple, treatment is in place for the C++ code present in rootmaps.