I have some regex expressions that I want to put into my R package documentation:
this <- c("letter-number"="^([a-zA-Z]{1}[0-9]+)")
When I put this into the roxygen doc strings as
#' @details This is the regex schema that I use: "`r this`".
#' @export
this <- c("letter-number"="^([a-zA-Z]{1}[0-9]+)")
it gets rendered as ^([a-zA-Z]10-9+), i.e. the curly brackets are absorbed / the expression inside the curly brackets is evaluated. Looking at the compiled .Rd file, I suspect it is the problem of the help file rendering, as in that file, the line shows up as "^([a-zA-Z]{1}\link{0-9}+)" (although it is problematic that roxygen has converted the square brackets to the \link{} instruction; it gets ignored when I view the help file with ?this).
What is an appropriate way to display this kind of string verbatim?
> packageVersion("roxygen2")
[1] ‘7.1.2’
> packageVersion("devtools")
[1] ‘2.4.3’
> packageVersion("glue")
[1] ‘1.6.2’
(I am stuck with a dated R 4.1.2 at the moment.)
While this might be a bug in roxygen2 (or its use of rmarkdown), if you can tolerate a helper-function, then we can do this:
backticks <- function(z) paste0('`', z, '`')
#' This.
#' @details This is the regex schema that I use: "`r backticks(this)`".
#' @export
this <- c("letter-number"="^([a-zA-Z]{1}[0-9]+)")
Rendered with devtools::document() (among other ways, same-effect) results in this in the man/this.Rd file:
\details{
This is the regex schema that I use: "\verb{^([a-zA-Z]\{1\}[0-9]+)}".
}
which renders as
Details:
This is the regex schema that I use: "^([a-zA-Z]{1}[0-9]+)".
For context, R-4.2.3 in emacs/ESS with
packageVersion("roxygen2")
# [1] '7.2.3'
packageVersion("devtools")
# [1] '2.4.5'
packageVersion("rmarkdown")
# [1] '2.20'
packageVersion("glue")
# [1] '1.6.2'