[R-pkg-devel] if statements in NAMESPACE file

Hello,


I'm updating my package 'this.path' which is supposed to retrieve the
absolute path of the executing script when called. It's similar to 'here',
except that 'here' constructs paths relative to a project directory,
whereas 'this.path' constructs paths relative to script directories. I was
updating the section where I retrieve the executing script's path while
running from a script open in Rgui for Windows, and I needed
utils::getWindowsHandles to do such a thing. But utils::getWindowsHandles
is a Windows only function, I
would imagine that 'utils' contains a similar line of code as above:


if (.Platform$OS.type == "windows")
   getWindowsHandles <- function() ...


and then in the NAMESPACE:


if (.Platform$OS.type == "windows")
   export(getWindowsHandles)


so I'd like to change my code to getWindowsHandles and import
getWindowsHandles from utils, but I can only do that on Windows, and so the
conditional importing should work for me. At no point does my function
mis-behave because of a attempting to use a function that isn't exported on
that platform, because within the function it only uses getWindowsHandles
if the OS is Windows.


On Thu, Sep 30, 2021 at 11:01 AM Mark Miller <mark.roman.miller at gmail.com>
wrote:

Returning to the original question, if it's helpful: I'd like to know what
constraints led to considering an export only available on Windows, and see
if we can suggest some other designs. It'd be good to keep the user's
mental model abstracted from the platform they're working on. There are
often unavoidable differences due to platform, but usually they're handled
with warnings and errors rather than selective exports.

On Thu, Sep 30, 2021 at 3:40 AM Berry Boessenkool <
berryboessenkool at hotmail.com> wrote:

One of the very best fortunes nominations!

[...]

  I suspect something like

   if (stats::runif(1) > 0.5) export(someFunction)

would work too, for a particularly frustrating experience for your
users.  It would mean half the installs export the function, and half
don't.

Duncan Murdoch


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