Documentation: how to use r or r_bg in a package to call other package functions

[daattali]

Suppose I'm developing a package mypkg that has a function myfxn() that makes a call to another internal (ie not exported) function:

#' @export
myfxn <- function() {
  some_slow_fxn()
}

Because this is slow, I want to run it in a background process asynchly. So I naively tried

#' @export
myfxn <- function() {
  callr::r_bg(function() some_slow_fxn())
}

But this doesn't work because could not find function "some_slow_fxn"

I could use myfxn:::some_slow_fxn instead, but then CRAN would cry, and so would I.

I could probably pass in the function itself as an argument, but that seems terrible. There must be a proper solution that I'm somehow overlooking, but I couldn't find any info in the documentation about how to use in a package.

[gaborcsardi]

#' @export
myfxn <- function() {
  callr::r_bg(function() asNamespace("mypkg")$some_slow_fxn())
}

You might still cry, but it gets the job done...

It would possibly make sense to make it easier to use the package's namespace in the subprocess, i.e. calling your own function in the subprocess, but currently there is nothing like that. In fact, callr makes an effort not to load any packages in the subprocess, as a "clean" environment is another frequent use case.

[daattali]

I fully support the decision to have a clean environment. My usecase here is definitely less common. If you think it's common enough then I can change this issue from a "documentation request" to a feature request, otherwise you can close this

[gaborcsardi]

Yeah, we can keep it open, I'll have a new release in a week or so, and then look at this again. Documenting it is not great, because it is essentially a receipt to go around an R CMD check warning. Even though I think in this case it should be considered a false positive.

But maybe I can support it somehow, via an extra argument to r() and r_bg(), etc. It is actually a use case that comes of often in my packages.

[daattali]

If it could be supported by a parameter to r/r_bg that would be a nice addition. Changed the issue title.

[gaborcsardi]

Probably the best is to document this, I decided. :)

[daattali]

Sounds good. I've run out of tears, I won't cry over this solution anymore :)