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

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/
        >>
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        >>
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        >>

        >

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