Writing S3 head() methods

a note to self for later

I’ve been struggling for the past 15-20 minutes trying to fix the following R CMD check greivances.

checking whether the namespace can be loaded with stated dependencies ... WARNING
  Error: object 'head' not found whilst loading namespace 'arcgislayers'
  Execution halted

checking dependencies in R code ... NOTE
  Error: object 'head' not found whilst loading namespace 'arcgislayers'

It feels like something that shouldn’t be difficult? You write the method and you export it right? Well, that’s true if the function is exported in base. But there are a lot of handy functions that are in base R that are not in the package {base}.

head(), the function I’m fighting with, is actually an export of the base R package {utils}.

Here’s some code I have that I couldn’t get to export head() properly.

#' @export
head.FeatureLayer <- function(x, n = 6, token = Sys.getenv("ARCGIS_TOKEN"), ...) {
  collect_layer(x, n_max, token)
}

To fix this we need to do the following:

1. Add utils as an imported package with usethis::use_package("utils")
2. Then we need to specifically import head by adding #' @importFrom utils head
3. Redocument with devtools::document() (or cmd + shift + d)

The whole shebang:

#' @importFrom utils head
#' @export
head.FeatureLayer <- function(x, n = 6, token = Sys.getenv("ARCGIS_TOKEN"), ...) {
  collect_layer(x, n, token)
}

Now R CMD check won’t complain about it.