R devel - Oct 2006 - Getting hold of a package's environment from C code

Hi,

I have a package where I'm calling an R function (say "foo") from
C
code. "foo" is in the same package, but is not exported. I construct
the call using lang1(install("foo")), but to eval it I need the
package's environment.  Is there a way to do this? Passing the correct
environment through .Call() is not an option.

Right now, I'm getting the environment first using something like

  rho = PROTECT(eval(lang2(install("environment"),
install("bar")),
R_GlobalEnv))

where bar _is_ exported. However, this doesn't work if the package is
loaded but not attached, and is also risky because someone might
define another "bar" that is found first.

One solution that might work is to make 'rho' a global variable and
assign the correct value when the package is loaded. Is that a good
idea? How should I PROTECT it?

-Deepayan

On 10/22/2006 3:56 PM, Deepayan Sarkar wrote:
> Hi,
> 
> I have a package where I'm calling an R function (say "foo")
from C
> code. "foo" is in the same package, but is not exported. I
construct
> the call using lang1(install("foo")), but to eval it I need the
> package's environment.  Is there a way to do this? Passing the correct
> environment through .Call() is not an option.
> 
> Right now, I'm getting the environment first using something like
> 
>   rho = PROTECT(eval(lang2(install("environment"),
install("bar")),
> R_GlobalEnv))
> 
> where bar _is_ exported. However, this doesn't work if the package is
> loaded but not attached, and is also risky because someone might
> define another "bar" that is found first.
In R code, you could use getNamespace("pkg") to get the namespace 
environment.  I haven't tried this, but I'd assume

PROTECT(rho = eval(lang2(install("getNamespace"),
                          ScalarString(mkChar("pkg"))));

(or something like it) would be the C equivalent.

 >
 > One solution that might work is to make 'rho' a global variable
and
 > assign the correct value when the package is loaded. Is that a good
 > idea? How should I PROTECT it?

I'd say to avoid globals if you can, and I think you can here.

Duncan Murdoch