The type of external pointers
EXTPTRSXP.Rd
EXTPTRSXP is an object-like macro defining the SEXPTYPE
type of external pointer objects.
Declaration
#define EXTPTRSXP 22 /* external pointer */
In Rinternals.h.
References
https://cran.r-project.org/doc/manuals/r-patched/R-ints.html#SEXPTYPEs