Global variables

Hi Sebastian,

You might also find the proto package useful as a way of restricting
the scope of variables. It provides a more intuitive (at least to me)
way of packaging variables and functions up into environments that can
be related in a hierarchy.

Michael

On 10 January 2011 23:48, Sebastien Bihorel
<Sebastien.Bihorel at cognigencorp.com> wrote:
  

Thank Gabor and Duncan,

That will be helpful.

Gabor Grothendieck wrote:
    

On Thu, Jan 6, 2011 at 4:59 PM, Duncan Murdoch <murdoch.duncan at gmail.com> wrote:

      

On 06/01/2011 4:45 PM, Sebastien Bihorel wrote:

        

Dear R-users,

Is there a way I can prevent global variables to be visible within my
functions?

          

Yes, but you probably shouldn't.  You would do it by setting the environment
of the function to something that doesn't have the global environment as a
parent, or grandparent, etc.  The only common examples of that are baseenv()
and emptyenv().  For example,

x <- 1
f <- function() print(x)

Then f() will work, and print the 1.  But if I do

environment(f) <- baseenv()

then it won't work:


        

f()

          

Error in print(x) : object 'x' not found

The problem with doing this is that it is not the way users expect functions
to work, and it will probably have weird side effects.  It is not the way
things work in packages (even packages with namespaces will eventually
search the global environment, the namespace just comes first).  There's no
simple way to do it and yet get access to functions in other packages
besides base without explicitly specifying them (e.g. you'd need to use
stats::lm(), not just lm(), etc.)


        

A variation of this would be:

environment(f) <- as.environment(2)

which would skip over the global environment, .GlobEnv, but would
still search the loaded packages.  In the example above x would not be
found but it still could find lm, etc.



      

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