[R-pkg-devel] Is there a better way ...?

[Rolf Turner]

On Thu, 21 Oct 2021 02:03:41 -0400
Duncan Murdoch <murdoch.duncan using gmail.com> wrote:

> On 21/10/2021 12:40 a.m., Andrew Simmons wrote:
> > I think the simplest answer is to store the variable in the
> > functions frame. I'm assuming here that the only plot.foo needs
> > access to .fooInfo, if not this can be changed.
> > 
> > 
> > plot.foo <- function (...)
> > {
> >      .fooInfo
> > }
> > environment(plot.foo) <- new.env()
> > evalq({
> >      .fooInfo <- NULL
> > }, environment(plot.foo))
> > 
> > 
> > Make your function, and do whatever you need with .fooInfo within
> > said function. Whenever you previously updated .fooInfo in the
> > global environment, update .fooInfo in plot.foo environment instead.
> > Also, because .fooInfo is not stored in the package's frame, it
> > won't be locked when the namespace is sealed. If you created it at
> > the toplevel, that would create some issues. But this works fine.
> 
> I agree with the final result, but I'd write the code differently:
> 
> plot.foo <- local({
> 
>    .fooInfo <- NULL
> 
>    function (...) { ... }
> })
> 
> creates an environment, puts .fooInfo into it with value NULL, then 
> creates a function with that environment attached and returns it.
> 
> I think Andrew's approach will work, but changing a function's 
> environment always worries me.  Using local(), the function assigned
> to plot.foo never has a different environment than the one it ends up
> with (and I don't need to remember how evalq() works).

Thanks everyone for these suggestions.  They seem a great deal
less shaganappi/kludgy than my previous approaches.

I've never really felt totally comfortable with the environment
concept, despite have used it quite a bit (basically in a
hammer-and-hope style.)

Can anyone comment on the difference between Deepayan's suggestion
(create a new environment in the package) and Duncan's suggestion
(create an environment that is local to plot.foo())?  Are there pros
and cons between the two?

And Deepayan:  what is the rationale for not exporting the new
environment that you suggest creating?  Presumably this guards against
something.  What?  I'd just like to extend my (currently minimal)
comprehension of the issues.

I must admit that Andrew's suggestion kind of overwhelms and bewilders
me.  I really have no idea what evalq() does.  I guess I could RTFM,
but the thought of doing that scares me! :-)

Thanks again everybody.

cheers,

Rolf

-- 
Honorary Research Fellow
Department of Statistics
University of Auckland
Phone: +64-9-373-7599 ext. 88276