[R] Global variables

[Gabor Grothendieck]

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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