[Rd] Exiting R and package detachment?

[Prof Brian Ripley]

Note that you can terminate R via q() without running .Last, and indeed 
how R is terminated is up to the front-end in use.  So the answer to

> is there away to assure that a package is detached when R quits?

is `No'.

On Fri, 10 Jun 2005, Henrik Bengtsson wrote:

> 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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>
>

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595