conditionally import a namespace?

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

"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

"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)
   ....
   ....
}

??

On 10/30/2008 10:15 AM, Martin Maechler wrote:

"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)
   ....
   ....
}

??

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.

On 10/30/2008 10:15 AM, Martin Maechler wrote:

"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)
  ....
  ....
}

??

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.

Duncan Murdoch

On 10/30/2008 10:44 AM, Duncan Murdoch wrote:

On 10/30/2008 10:15 AM, Martin Maechler wrote:

"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)
  ....
  ....
}

??

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