How to check platform in .onLoad in the R package

Question

I am trying to check if the package is run on Windows during the loading of the package and load some additional files. For some reason this doesn't work (added to my zzz.R):

.onLoad <- function(libname, pkgname){
    if(.Platform$OS.type == "windows") {
        # do specific task here
    }
}

How to make it work, is there a better way to do it?

Answer 1

EDIT to correct a wrong previous answer

After loading, loadNamespace looks for a hook function named .onLoad and calls it. The functions loadNamespace is usually called implicitly when library is used to load a package. However you can be useful at times to call these functions directly. So the following(essentially your code) works for me under windows platform.

.onLoad <- function(libname, pkgname ) {
    if(.Platform$OS.type == "windows")  print("windows")
    else print("others")
}

Then you test it using:

loadNamespace("loadpkg")
[1] "windows"
<environment: namespace:loadpkg>

Note also you can have the same thing using library, but you should unload the namespace before (I guess it checks if the package is already loaded and don't call all hooks):

unloadNamespace("loadpkg")
library("loadpkg")
[1] "windows"

don't use this , it is a wrong but accepted solution

You should initialize function parameters:

.onLoad <- function(libname = find.package(pkg_name), pkgname = pkg_name){
 if(.Platform$OS.type == "windows") {
    # do specific task here
  }
}