[R] Example for Roxygen @eval tag?

[Boris Steipe]

Yes, that's where I started -  the vignette says:

    ... Run arbtirary R code with @eval.

    ... the @eval tag. It evaluates code and treats the result as if it
    was a literal roxygen tags. This makes it possible to eliminate
    duplication by writing functions.

The first thing I noticed was that it does not say anything about delimiters. By trial and error it seems to consider everything up to the next @... tag in the header. Things that are not R code create an error during devtools::document() processing. It seems the output is captured and processed, i.e. System.time() creates a not-a-string error, but as.character(System.time()) passes ... but then nothing appears in the .Rd - and I haven't been able to find a single example of @eval in use in the wild.

No joy.




> On 2019-04-22, at 01:29, Jeff Newmiller <jdnewmil using dcn.davis.ca.us> wrote:
> 
> I have not used it... but did you read the vignette [1]? It sounds like it is a bit more meta than you think it is...
> 
> [1] https://cran.r-project.org/web/packages/roxygen2/vignettes/rd.html
> 
> On April 21, 2019 7:44:17 PM PDT, Boris Steipe <boris.steipe using utoronto.ca> wrote:
>> Playing with Roxygen features, but can't get @eval to work. E.g. ...
>> 
>> #' @eval sprintf("%s", Sys.time())
>> 
>> ... does not do what I thought it would (i.e. substitute the tag and
>> the expression with the string). Instead I see nothing in the .RD file.
>> 
>> Any working examples out there?
>> Thanks!
>> Boris
>> 
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> 
> -- 
> Sent from my phone. Please excuse my brevity.