Hi,
is there away to assure that a package is detached when R quits? I know
about .Last(), but that requires the user to setup that function. What
I am looking for is a way for the package to do this itself, without
asking the user to edit "their" .Last(). From ?setHook I know that:
"...when an R is finished, packages are not detached and namespaces
are not unloaded, so the corresponding hooks will not be run."
I am going to use this to load settings from file when a package loads
and automatically save (by optionally prompting the user) them back to
file when the package is no longer available (==detached/unloaded/R
quits). I am currently loading the settings in .First.lib() and have
code in .Last.lib() to save them.
Are there other ways to assure functions to be called when R quits? The
best I can think of now is to "hack" .Last() by doing something like
if (!exists(".LastOriginal", mode="function")) {
.LastOriginal <<- get(".Last", envir=.GlobalEnv);
.Last <<- function(..., envir=parent.frame()) {
for (fun in getHook(".Last")) {
if (is.character(fun))
fun <- get(fun, mode="function")
try(fun());
}
eval(.LastOriginal(...), envir=envir);
} # .Last()
}
Then in package <pkg>:
.First.lib <- function(libname, pkgname) {
# Detach package when R finishes.
setHook(".Last", function(...) {
pos <- match(paste("package:", pkgname, sep=""), search());
if (!is.na(pos))
detach(pos=pos);
})
}
However, this will be broken if user redefines .Last(). What about
defining a hook "onSessionExit" to be called before (after?) .Last() is
called. In analogue to on.exit() one could then define
onSessionExit <- function(fcn, ...) {
setHook("onSessionExit", fcn, ...);
}
Just curious, the above quote makes me wonder what is the rational for
the behavior? Was it made on purpose or is it simply just easier for R
to finish without detaching/unloading packages first? In what
situations to you have "clean-up" code for a package that is only called
when detach("package:<pkg>") is used? One situation I can imaging is
when a bundle of packages are loaded and when you detach the package
that all other packages requires, the other packages are also detached
for conveniency.
Best wishes
Henrik
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