> > On Nov 24, 2011, at 14:05 , Matthew Dowle wrote: > >> Since list() is primitive I tried to construct a data.frame starting >> with >> list() [since structure() isn't primitive], but then merely adding an >> attribute seems to set NAMED==2 too ? > > Yes. As soon as there is the slightest risk of having (had) two references > to the same object NAMED==2 and it is never reduced. While your mind is > boggling, I might boggle it a bit more: > >> z <- 1:10 >> .Internal(inspect(z)) > @116e11788 13 INTSXP g0c4 [NAM(1)] (len=10, tl=0) 1,2,3,4,5,... >> m <- mean(z) >> .Internal(inspect(z)) > @116e11788 13 INTSXP g0c4 [NAM(2)] (len=10, tl=0) 1,2,3,4,5,... > > This happens because while mean() is running, there is a second reference > to z, namely mean's argument x. (With languages like R, you have no > insurance that there will be no changes to the global environment while a > function call is being evaluated, so bugs can bite in both places -- z or > x.) > > There are many of these cases where you might pragmatically want to > override the default NAMED logic, but you'd be stepping into treacherous > waters. Luke has probably been giving these matters quite some thought in > connection with his compiler project.
Ok, very interesting. Think I'm there. Thanks for all the info. Matthew ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
