[R-pkg-devel] Force namespace prefix for a loaded package function

[Duncan Murdoch]

On 27/06/2016 5:46 PM, Tim Keitt wrote:
>
>
> http://www.keittlab.org/
>
> On Mon, Jun 27, 2016 at 10:19 AM, Duncan Murdoch
> <murdoch.duncan at gmail.com <mailto:murdoch.duncan at gmail.com>> wrote:
>
>     On 27/06/2016 11:08 AM, Tim Keitt wrote:
>
>         http://www.keittlab.org/
>
>         On Mon, Jun 27, 2016 at 3:22 AM, Joris Meys <jorismeys at gmail.com
>         <mailto:jorismeys at gmail.com>> wrote:
>
>         > If you want to call a non exported function, you need three colons
>         >
>         > X:::f ()
>         >
>         > And frankly, that is a bad idea.
>         >
>         I think you missed the point (and stated the obvious).
>
>         A well-designed namespace feature would give control of imports
>         to the code
>         user, not the code writer.
>
>         Right now, I have to avoid all the function names in base
>         because I will
>         cause a collision. If I want to have an "options" function in my
>         package, I
>         have to make it "pkgname_options" rather than pkgname::options,
>         which is
>         greatly preferable and would allow the user to decide whether
>         they want to
>         import it and then simply use "options" and "base::options".
>
>         I've always considered this all-or-nothing approach to imports a
>         bug in the
>         implementation of namespaces in R. I was trying to suggest that
>         it be
>         fixed. (Probably should have sent this to r-devel actually.)
>
>
>     The base package is special, but for all other packages there's no
>     "all-or-nothing" approach to imports, so your statement about a
>     function named "options" doesn't really make sense.  If you want to
>     do that, just do it, and other packages that prefer your
>     implementation to the base one can import just that one function, or
>     do the import at run time by calling it as pkgname::options().
>
>
> I know that. I mean for someone writing a script, not a package.
>
> Its all good for package writers. Its quite simple to control imports
> there. But not so much for someone using the package in R to write a
> script. You either go with package_name::object for everything or you
> call "library" and you get everything the packager exported.
>
> It would be nice to 1) be able to hold back some functions from being
> fully exported in a package and (maybe or) 2) extend the functionality
> of the NAMESPACE file to the user session via a set of functions.
>
> Does that make any more sense?

It makes a little more sense, but it's still not correct.  If you want 
to do the equivalent of importing foo::options, just add the line

options <- foo::options

at the start of your script.  This "imports" that one function, and 
nothing else from the foo namespace.

It has the side effect of leaving the options object in the current 
workspace afterwards.  If that concerns you, use local():

local( {
   options <- foo::options
   # Lots of calculations, computing result
   result
})

Duncan Murdoch


>
> THK
>
>
>
>     Duncan Murdoch
>
>
>         THK
>
>
>
>         > Cheers
>         > Joris
>         > On 26 Jun 2016 19:37, "Tim Keitt" <tkeitt at utexas.edu
>         <mailto:tkeitt at utexas.edu>> wrote:
>         >
>         >> It would be rather nice if we could define functions in our
>         packages that
>         >> must be called with the namespace prefix.
>         >>
>         >> I'd like to do
>         >>
>         >> #' @protected (or some such)
>         >> f = function(...) list(...)
>         >>
>         >> in package scope and then
>         >>
>         >> library(x)
>         >> f(1)             # fails
>         >> x::f(1)         # succeeds
>         >>
>         >> Currently unless I am missing something, a function is either
>         exported to
>         >> global scope or not available. This could be done if package
>         loading made
>         >> two environments, one in the path and another not in the
>         path, and then
>         >> have the namespace prefix search both in succession.
>         >>
>         >> Yes, you could do
>         >>
>         >> #' @export
>         >> x_f = function(...) list(...)
>         >>
>         >> library(x)
>         >> x_f(1)
>         >>
>         >> but I would prefer reusing the namespace prefix syntax.
>         >>
>         >> This would also avoid name collisions between package, which
>         ideally is
>         >> the
>         >> purpose of a namespace.
>         >>
>         >> I suppose also you could make two packages and list one in
>         Imports: but I
>         >> find that less satisfying because it requires a different
>         namespace
>         >> prefix.
>         >>
>         >> Or am I missing something obvious here.
>         >>
>         >> THK
>         >>
>         >> http://www.keittlab.org/
>         >>
>         >>         [[alternative HTML version deleted]]
>         >>
>         >> ______________________________________________
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>         >>
>         >
>
>                 [[alternative HTML version deleted]]
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