data.table allocates over alloc.col limit with [,:= but not set() #1831

library(data.table)

# make one-column test DT
DT<-data.table(V1=1:10)
# make 99 more columns with set()
for(x in 2:100){
  set(DT,NULL,paste0("V",x),1:10)
}
# make 101st column with set
set(DT,NULL,"V101",1:10) # does not work
# make 101st column with [,:=
DT[,V101:=1:10] # works

# using set vs. [,:= to make the first 99
# columns does not matter:

# make one-column test DT
DT<-data.table(V1=1:10)
# make 99 more columns with [,:=]
DT[,(paste0("V",2:100)):=1:10]
# make 101st column with set
set(DT,NULL,"V101",1:10) # does not work
# make 101st column with [,:=
DT[,V101:=1:10] # works

# order does not matter:

# make one-column test DT
DT<-data.table(V1=1:10)
# make 99 more columns with [,:=]
DT[,(paste0("V",2:100)):=1:10]
# make 101st column with [,:=
DT[,V101:=1:10] # works

# but, once having used [,:= one can
# again use set():
# make 102nd column with set
set(DT,NULL,"V102",1:10) # works