The type of weak references
WEAKREFSXP.Rd
WEAKREFSXP is an object-like macro defining the SEXPTYPE
type of weak reference objects.
Declaration
#define WEAKREFSXP 23 /* weak reference */
In Rinternals.h.
References
https://cran.r-project.org/doc/manuals/r-patched/R-ints.html#SEXPTYPEs