Monday 2 December 2019

r - How to properly document S4 class slots using Roxygen2?



For documenting classes with roxygen(2), specifying a title and description/details appears to be the same as for functions, methods, data, etc. However, slots and inheritance are their own sort of animal. What is the best practice -- current or planned -- for documenting S4 classes in roxygen2?



Due Diligence:



I found mention of an @slot tag in early descriptions of roxygen.
A 2008 R-forge mailing list post
seems to indicate that this is dead,
and there is no support for @slot in roxygen:



Is this true of roxygen2? The previously-mentioned post suggests a user should instead make their own itemized list with LaTeX markup. E.g. a new S4 class that extends the "character" class would be coded and documented like this:



#' The title for my S4 class that extends \code{"character"} class.
#'
#' Some details about this class and my plans for it in the body.
#'
#' \describe{
#' \item{myslot1}{A logical keeping track of something.}
#'
#' \item{myslot2}{An integer specifying something else.}
#'
#' \item{myslot3}{A data.frame holding some data.}
#' }
#' @name mynewclass-class
#' @rdname mynewclass-class
#' @exportClass mynewclass
setClass("mynewclass",
representation(myslot1="logical",
myslot2="integer",
myslot3="data.frame"),
contains = "character"
)


However, although this works, this \describe , \item approach for documenting the slots seems inconsistent with the rest of roxygen(2), in that there are no @-delimited tags and slots could go undocumented with no objection from roxygenize(). It also says nothing about a consistent way to document inheritance of the class being defined. I imagine dependency still generally works fine (if a particular slot requires a non-base class from another package) using the @import tag.



So, to summarize, what is the current best-practice for roxygen(2) slots?



There seem to be three options to consider at the moment:





  • A -- Itemized list (as example above).

  • B -- @slot ... but with extra tags/implementation I missed. I was unable to get @slot to work with roxygen / roxygen2 in versions where
    it was included as a replacement for the itemized list in the example
    above. Again, the example above does work with roxygen(2).

  • C -- Some alternative tag for specifying slots, like @param, that would accomplish the same thing.




I'm borrowing/extending this question from a post I made to the roxygen2 development page on github.


Answer





http://r-pkgs.had.co.nz/man.html#man-classes



I have not tried it yet for RC, but it works for me for S4 now.



Previously



It looks like S4 class slots are fully supported under Roxygen2 version 3.0+:



http://blog.rstudio.org/2013/12/09/roxygen2-3-0-0/



"document your S4 classes, S4 methods and RC classes with roxygen2 – you can safely remove workarounds that used @alias and @usage, and simply rely on roxygen2 to do the right thing."


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