[R-pkg-devel] active bindings in package namespace

[Kirill Müller]

Dear Jack


This doesn't answer your question, but I would advise against this design.

- Users do not expect side effects (such as network access) from 
accessing a symbol.

- A function gives you much more flexibility to change the interface 
later on. (Arguments for fetching the data, tokens for API access, ...)

- You already encountered a few quirks that make this an "interesting" 
problem.

A function call only needs a pair of parentheses.


Best regards

Kirill


On 23.03.19 16:50, Jack O. Wasey wrote:
> Dear all,
>
> I am developing a package which is a front for various online data 
> (icd.data https://github.com/jackwasey/icd.data/ ). The current CRAN 
> version just has lazy-loaded data, but now the package encompasses far 
> more current and historic ICD codes from different countries, these 
> can't be included in the CRAN package even with maximal compression.
>
> Other authors have solved this using functions to get the data, with 
> or without a local cache of the retrieved data. No CRAN or other 
> packages I have found after extensive searching use the attractive 
> active binding feature of R.
>
> The goal is simple: for the user to refer to the data by its symbol, 
> e.g., 'icd10fr2019', or 'icd.data::icd10fr2019', and it will be 
> downloaded and parsed transparently (if the user has already granted 
> permission, or after prompt if they haven't).
>
> The bindings are set using commands alongside the function definitions 
> in R/*.R .E.g.
>
> makeActiveBinding("icd10cm_latest", .icd10cm_latest_binding, 
> environment())
> lockBinding("icd10cm_latest", environment())
>
> For non-interactive use, CI and CRAN tests, no data should be 
> downloaded, and no cache directory set up without user consent. For 
> interactive use, I ask permission to create a local data cache before 
> downloading data.
>
> This works fine... until R CMD check. The following steps seems to 
> 'get' or 'source' everything from the package namespace, which results 
> in triggering the active bindings, and this fails if I am unable to 
> get consent to download data, and want to 'stop' on this error condition.
>  - checking dependencies in R code
>  - checking S3 generic/method consistency
>  - checking foreign function calls
>  - checking R code for possible problems
>
> Debugging CI-specific binding bugs is a nightmare because these occur 
> in different R sessions initiated by R CMD check.
>
> There may be legitimate reasons to evaluate everything in the 
> namespace, but I've no idea what they are. Incidentally, Rstudio also 
> does 'mget' on the whole package namespace and triggers bindings 
> during autocomplete. https://github.com/rstudio/rstudio/issues/4414
>
> Is this something I should raise as an issue with R? Or does anyone 
> have any idea of a sensible approach to this. Currently I have a set 
> of workarounds, but this complicates the code, and has taken an awful 
> lot of time. Does anyone know of any CRAN package which has active 
> bindings in the package namespace?
>
> Any ideas appreciated.
>
> Jack Wasey
>
> ______________________________________________
> R-package-devel using r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-package-devel