Just to note, S4 classes can be defined to extend symbols (class "name") and other reference types. These work by using a hidden slot for the reference object, just to avoid attaching attributes to the reference. (Discussed briefly in the section on Basic Classes in ?Classes.)
John William Dunlap wrote: >> -----Original Message----- >> From: l...@stat.uiowa.edu [mailto:l...@stat.uiowa.edu] >> Sent: Friday, March 12, 2010 4:24 PM >> To: William Dunlap >> Cc: r-devel@r-project.org >> Subject: Re: [Rd] symbol name caching bug: attributes get >> tied to symbol names >> >> Since symbols/names are reference objects this behavior in unavoidable >> if we allow attributes to be added to them. On the other hand, I'm >> not sure it makes sense to allow that. Attempting to set an attribute >> on NULL signals an error; it would probably make sense to do the same >> for any name object. >> >> > > Thanks Luke, for the explanation. > > I'm comfortable disallowing attributes on names. > > The problem arose for me when analyzing a parse > tree and I was using attributes to label parts of it. > I can stick in a list() layer above the calls, names, > etc., to attach the attributes to. That can simplify > the syntax also, since things like as.vector() applied > to a call object with attributes won't strip the attributes. > > Bill Dunlap > Spotfire, TIBCO Software > wdunlap tibco.com > > >> luke >> >> On Fri, 12 Mar 2010, William Dunlap wrote: >> >> >>> In R versions 2.10.1 and "2.11.0 Under development >>> (unstable) (2010-03-07 r51225)" on Windows I get the >>> following if I type the commands at the start of >>> the session. Note how the attribute attached to >>> the name "Response" by the initial call to structure() >>> seems to get tied to that name for the remainder of >>> the session: >>> >>> > z <- structure(quote(Response), isResponse=TRUE) >>> > parse(text="Response~Predictor")[[1]][[2]] >>> Response >>> attr(,"isResponse") >>> [1] TRUE >>> > quote(Response~Predictor)[[2]] >>> Response >>> attr(,"isResponse") >>> [1] TRUE >>> > quote(Response) >>> Response >>> attr(,"isResponse") >>> [1] TRUE >>> >>> The attribute actually does go away after quite a >>> while, but I haven't figured out the trigger. >>> rm(z) followed by gc() does not affect it. >>> >>> If I use an unadorned variable called Response before >>> making the structure z, then the isResponse attribute >>> doesn't seem to stick to the name Response. >>> >>> >>> Bill Dunlap >>> Spotfire, TIBCO Software >>> wdunlap tibco.com >>> >>> ______________________________________________ >>> R-devel@r-project.org mailing list >>> https://stat.ethz.ch/mailman/listinfo/r-devel >>> >>> >> -- >> Luke Tierney >> Chair, Statistics and Actuarial Science >> Ralph E. Wareham Professor of Mathematical Sciences >> University of Iowa Phone: 319-335-3386 >> Department of Statistics and Fax: 319-335-3017 >> Actuarial Science >> 241 Schaeffer Hall email: l...@stat.uiowa.edu >> Iowa City, IA 52242 WWW: http://www.stat.uiowa.edu >> >> > > ______________________________________________ > R-devel@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-devel > > [[alternative HTML version deleted]] ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
