From J.C.Rougier@durham.ac.uk  Fri May  3 11:49:25 2002
From: J.C.Rougier@durham.ac.uk (Jonathan Rougier)
Date: Fri, 03 May 2002 11:49:25 +0100
Subject: [Rd] Behaviour of environment(foo)<- (PR#1509)
References: <200205031012.MAA13485@pubhealth.ku.dk> <x26625y1al.fsf@blueberry.kubism.ku.dk>
Message-ID: <3CD26B35.1F72FD86@durham.ac.uk>

Peter Dalgaard BSA wrote:
> 
> J.C.Rougier@durham.ac.uk writes:
> 
> > Hi Everyone,
> >
> > I've noticed that setting the environment of a function from a package
> > actually creates a copy of that function in .GlobalEnv and sets the
> > environment on this copy:
> >
> > > find(.profile)
> > [1] "package:newblips"
> > > environment(.profile) <- bb1$getEnv() # this is an environment
> > > find(.profile)
> > [1] ".GlobalEnv"       "package:newblips"
> >
> > I don't have a problem with this behaviour (now I understand it!) but
> > I think that it would help to document it in the help file.  May I
> > suggest that instead of
> >
> >      The assignment form sets the environment of the function or
> >      formula `fun' to the `value' given.
> >
> > we have
> >
> >      The assignment form sets the environment of the function or
> >      formula \code{fun} to \code{value} if \code{fun} is in the
> >      current environment, otherwise it makes a copy of \code{fun} in
> >      the current environment and sets the environment of the copy.
> >
> > I think that describes the current procedure: please correct me if I
> > am wrong!
> 
> But this is generic behaviour for *all* attribute assignment. It makes
> no sense to describe a specific instance of it. Consider
> 
> data(airquality)
> f<-function() { x <- class(airquality)<-NULL; ls() }
> f()
> class(airquality)

I understand.  However, I still think that the help page for environment
is wrong!  Using "enviroment<-" does not necessarily set the environment
of the function, as stated.  What happened to me is that I modified
.profile in the package newblips and then re-assigned its environment
but didn't see any change, because it was masked by the copy of .profile
in .GlobalEnv that I didn't know I had.  That's quite a subtle outcome
and I think that changing the environment help page would clarify this
for other users.  J.

-- 
Jonathan Rougier                       Science Laboratories
Department of Mathematical Sciences    South Road
University of Durham                   Durham DH1 3LE
tel: +44 (0)191 374 2361, fax: +44 (0)191 374 7388
http://www.maths.dur.ac.uk/stats/people/jcr/jcr.html
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[Rd] Behaviour of environment(foo)<- (PR#1509)
Jonathan Rougier