R devel - Jul 2006 - attributes of environments

In the code below, e is an environment which we copy to f and then
add attributes to e.  Now f winds up with the same attributes.

In other words it seems that the attributes are a property of the
environment itself and not of the variable.  Thus it appears we
cannot have two environment variables that correspond to the
original environment but with different attributes.

I can understand if we changed a component of e then
f would reflect that too but I am not sure that this is also
desirable for attributes as they are not "in" the environment.

Is that desirable?  Is it a bug?  No other class works that way
AFAIK.   Comments?
> e <- new.env()
> f <- e
> attr(e, "X") <- "Y"   # X is an attribute of e
> f  # f gets the same attribute !!!
<environment: 0x01a577f0>
attr(,"X")
[1] "Y"
> R.version.string # Windows XP
[1] "R version 2.4.0 Under development (unstable) (2006-07-04 r38480)"

On 7/4/2006 11:12 PM, Gabor Grothendieck wrote:
> In the code below, e is an environment which we copy to f and then
> add attributes to e.  Now f winds up with the same attributes.
> 
> In other words it seems that the attributes are a property of the
> environment itself and not of the variable.  Thus it appears we
> cannot have two environment variables that correspond to the
> original environment but with different attributes.
> 
> I can understand if we changed a component of e then
> f would reflect that too but I am not sure that this is also
> desirable for attributes as they are not "in" the environment.
> 
> Is that desirable?  Is it a bug?  No other class works that way
> AFAIK.   Comments?
I'm not sure about whether this is desirable or a bug, but environments 
are special, in that they are among the very few objects treated as 
references.  In your example, adding a variable to e will also make it 
visible in f.

Duncan Murdoch
> 
>> e <- new.env()
>> f <- e
>> attr(e, "X") <- "Y"   # X is an attribute of e
>> f  # f gets the same attribute !!!
> <environment: 0x01a577f0>
> attr(,"X")
> [1] "Y"
>> R.version.string # Windows XP
> [1] "R version 2.4.0 Under development (unstable) (2006-07-04
r38480)"
> 
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel

On Tue, 4 Jul 2006, Gabor Grothendieck wrote:
> In the code below, e is an environment which we copy to f and then
> add attributes to e.  Now f winds up with the same attributes.
>
> In other words it seems that the attributes are a property of the
> environment itself and not of the variable.  Thus it appears we
> cannot have two environment variables that correspond to the
> original environment but with different attributes.
No, we can't. The two variables are references to the same environment, so 
they are the same.

If you want the attributes to be copies rather than references then create 
a list with the environment as an element and put the attributes on the 
list.

 	-thomas

Thomas Lumley			Assoc. Professor, Biostatistics
tlumley at u.washington.edu	University of Washington, Seattle