>>>>> Henrik Bengtsson <henrik.bengts...@gmail.com> >>>>> on Thu, 1 Feb 2018 10:26:23 -0800 writes:
> On Thu, Feb 1, 2018 at 12:14 AM, Martin Maechler > <maech...@stat.math.ethz.ch> wrote: >>>>>>> Michael Lawrence <lawrence.mich...@gene.com> >>>>>>> on Tue, 30 Jan 2018 15:57:42 -0800 writes: >> >> > I just meant that the minimal contract for as.list() appears to be that it >> > returns a VECSXP. To the user, we might say that is.list() will always >> > return TRUE. >> >> Indeed. I also agree with Herv'e that the user level >> documentation should rather mention is.list(.) |--> TRUE than >> VECSXP, and interestingly for the experts among us, >> the is.list() primitive gives not only TRUE for VECSXP but >> also of LISTSXP (the good ole' pairlists). >> >> > I'm not sure we can expect consistency across methods >> > beyond that, nor is it feasible at this point to match the >> > semantics of the methods package. It deals in "class >> > space" while as.list() deals in "typeof() space". >> >> > Michael >> >> Yes, and that *is* the extra complexity we have in R (inherited >> from S, I'd say) which ideally wasn't there and of course is >> not there in much younger languages/systems such as julia. >> >> And --- by the way let me preach, for the "class space" --- >> do __never__ use >> >> if(class(obj) == "<classname>") >> >> in your code (I see this so often, shockingly to me ...) but rather use >> >> if(inherits(obj, "<classname>")) >> >> instead. > Second this one. But, soon (*) the former will at least give the > correct answer when length(class(obj)) == 1 > and produce an error > otherwise. Not quite; I think you you did not get the real danger in using 'class(.) == *': What you say above would only be true if there were only S3 classes! Try the following small R snippet myDate <- setClass("myDate", contains = "Date") ## Object of class "myDate" ## [1] "2018-02-02" (d <- myDate(Sys.Date())) class(d) == "Date" # is FALSE (hence of length 1) inherits(d, "Date") # is TRUE > So, several of these cases will be caught at run-time in a > near future. Maybe. But all the others are still wrong, as I show above. Martin > (*) When _R_CHECK_LENGTH_1_CONDITION_=true becomes the default > behavior - hopefully by R 3.5.0. >> >> Martin ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel