Hi Seth,
And thanks for your suggestion! I was not able to do exactly what you
described (I have no earlier experience with using environments), but
you mentioning .onLoad was a good starting point. I have now removed all
references to pkg1 from the NAMESPACE, and wrote the following .onLoad
function:
.onLoad <- function(libname, pkgname) {
if ("pkg1" %in% rownames(utils:::installed.packages()) ) {
library(pkg1)
info = matrix(c("fun1", "fun2", "fun3", rep("pkg2", 3), rep(NA,3)),
ncol = 3)
registerS3methods(info, package = "pkg1", env = environment(funInPkg2))
}
}
New methods for functions fun1, fun2 and fun3 seem to be available if
pkg1 is installed, while they are ignored if pkg1 is not installed. The
function above loads pkg1 automatically if installed (I would prefer
this to be optional), but at least it will not be necessary to download
pkg1 (with all its dependencies) for users without interest in it.
I have not found any description of registerS3methods (except from an
old .Rd file stating that it is not intended to be called directly), so
there might be better ways of doing this... And I am sure there is a
better way of assigning the right environment...
Thanks again,
Jon
Seth Falcon wrote:
Hi Jon,
* On 2009-06-30 at 15:27 +0200 Jon Olav Skoien wrote:
I work on two packages, pkg1 and pkg2 (in two different projects). pkg1 is
quite generic, pkg2 tries to solve a particular problem within same field
(geostatistics). Therefore, there might be users who want to use pkg2 as an
add-on package to increase the functionality of pkg1. In other words,
functions in pkg1 are based on the S3 class system, and I want pkg2 to
offer methods for pkg2-objects to functions defined in pkg1, for users
having both packages installed. Merging the packages or making pkg2 always
depend pkg1 would be the easiest solution, but it is not preferred as most
users will only be interested in one of the packages.
I'm not sure I understand the above, I think you may have a pkg2 where
you meant pkg1, but I'm not sure it matters.
I think the short version is, pkg2 can be used on its own but will do
more if pkg1 is available. I don't think R's packaging system
currently supports conditional dependencies as you might like.
However, I think you can get the behavior you want by following a
recipe like:
* In pkg2 DESCRIPTION, list Suggests: pkg1.
* In pkg2 code, you might define a package-level environment and
in .onLoad check to see if pkg1 is available.
PKG_INFO <- new.env(parent=emptyenv())
.onLoad <- function(libname, pkgname) {
if (check if pkg1 is available) {
PKG_INFO[["pkg1"]] <- TRUE
}
}
* Then your methods can check PKG_INFO[["pkg1"]].
+ seth
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