On 10/30/2008 10:44 AM, Duncan Murdoch wrote:
On 10/30/2008 10:15 AM, Martin Maechler wrote:
"FA" == Felix Andrews <[EMAIL PROTECTED]>
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)
....
....
}
??
I think the problem is that that puts the namespace on the user's search
list, which is what Felix wanted to avoid. He would like to
import(RGtk2), but only if it exists.
There are conditionals allowed in NAMESPACE files, but I don't know if
they are allowed to be used to control imports. They are not well
documented -- they were called "experimental" when introduced in 1.9.0.
If this is allowed, then something like
if( "RGtk2" %in% rownames(installed.packages()) ) {
import(RGtk2)
}
should work.
I just did a little test, and it does appear to work if you use
utils::installed.packages in the condition. And one clarification:
those lines go into your NAMESPACE file, not into R code.
Duncan Murdoch
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