From maechler at stat.math.ethz.ch  Thu Oct 30 15:15:06 2008
From: maechler at stat.math.ethz.ch (Martin Maechler)
Date: Thu, 30 Oct 2008 15:15:06 +0100
Subject: [Rd] conditionally import a namespace?
In-Reply-To: <94730b8a0810292340t7e328096u300e4a225e669c5d@mail.gmail.com>
References: <94730b8a0810292340t7e328096u300e4a225e669c5d@mail.gmail.com>
Message-ID: <18697.49514.201691.329789@stat.math.ethz.ch>

>>>>> "FA" == Felix Andrews <felix at nfrac.org>
>>>>>     on Thu, 30 Oct 2008 17:40:17 +1100 writes:

    FA> Dear R-devel,
    FA> I have a problem defining the dependencies for a package.

    FA> My package (latticist, not yet released) "Suggests" RGtk2, but
    FA> specifically does not require it. If RGtk2 is available, the user can
    FA> call a function that builds a GUI with RGtk2. However, I do not want
    FA> to attach the RGtk2 namespace, because it is irrelevant to the user
    FA> and exports about 7500 symbols.

    FA> Last time I asked a similar question to this, Professor Ripley noted
    FA> that the usual method to get around this situation is the use an
    FA> explicit package prefix to function calls (the `::` operator). But
    FA> this is not so easy with non-standard functions. Take this chunk of
    FA> code:

    FA> widg <- gtkComboBoxEntryNewText()
    FA> widg$show()
    FA> widg["width-request"] <- 100

    FA> The first call is easy to prefix, as RGtk2::gtkComboBoxEntryNewText()
    FA> but the others, `$.RGtkObject` and `[<-.RGtkObject` are not.

indeed.

    FA> While I *could* rewrite all the code to use explicit functions, I
    FA> think, the resulting code would be much less clear.

    FA> Essentially what I want to do is conditionally import the RGtk2 namespace.
    FA> Any suggestions?

Maybe something along the line of

if(is.function(try(RGtk2::gtkComboBoxEntryNewText))) {
   library(RGtk2)
   ....
   ....
}

??

Regards,
Martin



[Rd] conditionally import a namespace?
Martin Maechler