There are currently two global variables used by cytolib (mainly for troubleshooting purpose)
https://github.com/RGLab/cytolib/blob/trunk/inst/include/cytolib/global.hpp#L30-L31

extern keyword indicates they are only the variable declaration instead of definition. Because due to the nature of header-only, cytolib can't define them in any header in order to avoid multi-definition compiling errors (when header is included multiple times).

Therefore it implicitly requires the cytolib users to define it somewhere in the user code in order for cytolib function, even if they don't necessarily need to care about this log feature.

We shouldn't force user to do this (besides it is not best practice to use global variable). Instead, we can move them into GatingSet class and initialize/change their values either through parseWorkspace call or through setter methods once GatingSet is created.