How to export new generic function for new S3 class?

Question

I define a new function work_with_myS3 that is supposed to work with my new S3 class myS3:

work_with_myS3 = function (x) {
   UseMethod("work_with_myS3", x)
}

work_with_myS3.myS3 = function(x) {
   some code
}

When I source this in my normal R session (I'm using RStudio), it behaves exactly as expected. When I feed it an myS3 object, it works; when I feed it something strange, it throws an error:

> work_with_myS3(123)
Error in UseMethod("work_with_myS3", x) : 
  no applicable method for 'work_with_myS3' applied to an object of class "c('double', 'numeric')"

However, when I include this in my package, build it, reload it and try to call it:

Error: could not find function "work_with_myS3"

Help page works fine though, calling ?work_with_myS3. This is how I document it by devtools::document():

#' Do stuff with myS3
#'
#' What it does
#' @import dplyr
#' @param x object of class myS3
#' @method work_with_myS3 myS3
#' @export

There is also an entry in the namespace:

S3method(work_with_myS3,myS3)

Why is this, and how to make the function available in the package? I suspect I'm making some trivial mistake.

Answer 1

When you call work_with_myS3 with an object of class myS3 the UseMethod function looks for:

1. work_with_myS3.myS3 or
2. work_with_myS3.default

Therefore you need to export work_with_myS3.myS3, so

#' @export
work_with_myS3.myS3 = function(x) {
  ## do stuff
}

Alternatively, you could define a default method and export that.