R help - Jun 2002 - problems with assigning a class to an environment

I was surprised to find that calling str() on an environment can remove
attributes from it, as in
> a <- new.env()
> class(a) <- "jens"
> class(a)
[1] "jens"
> str(a)
Class 'jens' length 0 <environment>
> class(a)
NULL

then I found in the R-Language-Manual in chapter 2.1.10 Environments the
sentence: 

	"In particular, assigning attributes to an environment can lead to
surprises"

Can please someone familiar with the internals explain what's going on?

Is it save, to assign a class to a list which contains an environment?


Thank you


Jens Oehlschl?gel

> version
         _              
platform i386-pc-mingw32
arch     i386           
os       Win32          
system   i386, mingw32  
status                  
major    1              
minor    5.1            
year     2002           
month    06             
day      17             
language R 

-- 



-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
Send "info", "help", or "[un]subscribe"
(in the "body", not the subject !)  To: r-help-request at
stat.math.ethz.ch
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._

Jens Oehlschl?gel <joehl at gmx.de> writes:
> I was surprised to find that calling str() on an environment can remove
> attributes from it, as in
> 
> > a <- new.env()
> > class(a) <- "jens"
> > class(a)
> [1] "jens"
> > str(a)
> Class 'jens' length 0 <environment>
> > class(a)
> NULL
> 
> then I found in the R-Language-Manual in chapter 2.1.10 Environments the
> sentence: 
> 
> 	"In particular, assigning attributes to an environment can lead to
> surprises"
> 
> Can please someone familiar with the internals explain what's going on?
The main issue is that environments aren't copied on assignment, so
stuff like y <- unclass(x) will remove the class attribute from x if x
is an environment. Or, as is the case here, str(unclass(x)) will do it.

> Is it save, to assign a class to a list which contains an environment?
Yes, and the recommended way.

-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)             FAX: (+45) 35327907
-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
Send "info", "help", or "[un]subscribe"
(in the "body", not the subject !)  To: r-help-request at
stat.math.ethz.ch
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._