While poking around the C++ code in the dplyr package I ran across the idiom
Rf_defineVar(symbol, R_UnboundValue, environment)
to [sort of] remove 'symbol' from 'environment'
Using it makes the R-level functions objects(), exists(), and get()
somewhat inconsistent and I was wondering if that was intended. E.g., use
SHLIB to make something from the following C code that dyn.load can load
into R
% cat defineVarAsUnboundValue.c
#include <R.h>
#include <Rinternals.h>
SEXP defineVarAsUnboundValue(SEXP name, SEXP envir)
{
Rf_defineVar(name, R_UnboundValue, envir);
return R_NilValue;
}
erratic:bill:292% R-3.6.1 CMD SHLIB defineVarAsUnboundValue.c
gcc -std=gnu99 -I"/home/R/R-3.6.1/lib64/R/include" -DNDEBUG
-I/usr/local/include -fpic -g -O2 -c defineVarAsUnboundValue.c -o
defineVarAsUnboundValue.o
gcc -std=gnu99 -shared -L/home/R/R-3.6.1/lib64/R/lib -L/usr/local/lib64 -o
defineVarAsUnboundValue.so defineVarAsUnboundValue.o
-L/home/R/R-3.6.1/lib64/R/lib -lR
erratic:bill:293% R-3.6.1 --quiet --vanilla
dyn.load("defineVarAsUnboundValue.so")
envir <- list2env(list(One=1, Two=2))
objects(envir)
[1] "One" "Two"
.Call("defineVarAsUnboundValue", quote(Two), envir)
NULL
objects(envir)
[1] "One"
objects(envir, all.names=TRUE) # is "Two" a 'hidden' object?
[1] "One" "Two"
exists("Two", envir=envir, inherits=FALSE)
[1] TRUE
get("Two", envir=envir, inherits=FALSE) # get fails when exists says ok
Error in get("Two", envir = envir, inherits = FALSE) :
object 'Two' not found
Should Rf_defineVar(sym, R_UnboundValue, envir) remove sym from envir?
Bill Dunlap
TIBCO Software
wdunlap tibco.com