[Rd] Namespaces and S4 Generics

[Roger Koenker]

John,

Thanks very much.  As you suggested, this turned out not to have anything to do with R-devel.  Instead, it seemed traceable
to my decision a while back to start require()'ing packages in my .Rprofile, at least when I removed .Rprofile then my original
code for image methods worked fine in the current version of R-devel.  "Ours not to reason why..."  

Roger

url:    www.econ.uiuc.edu/~roger            Roger Koenker
email    rkoenker at uiuc.edu            Department of Economics
vox:     217-333-4558                University of Illinois
fax:       217-244-6678                Urbana, IL 61801

On Jul 11, 2014, at 8:35 PM, John Chambers <jmc at r-project.org> wrote:

> Roger,
> 
> Are you implying that your current code works differently under R-devel than with the current release?  Nothing I'm aware of would suggest that.
> 
> With or without setGeneric() (in either version but the single-argument is cleaner), a generic function for image() is created in your package's namespace.
> 
> If you don't export that function, calls from other functions in your package will still get the generic  version but calls from outside the package will get graphics::image.
> 
> Here's an example.  In my PkgA I have:
> 
> 	setGeneric("image")
> 
> 	setMethod("image", "A", function(x, ...) message("dummy image for class A"))
> 
> 	showStuff <- function() showMethods("image")
> 
> In the NAMESPACE, I exported showStuff, but not image.
> 
> As a result:
> 
>> require(PkgA)
> Loading required package: PkgA
>> image
> function (x, ...) 
> UseMethod("image")
> <bytecode: 0x7fa835170b08>
> <environment: namespace:graphics>
>> showMethods("image")
> 
> Function "image":
> <not an S4 generic function>
>> showStuff
> function () 
> showMethods("image")
> <environment: namespace:PkgA>
>> showStuff()
> Function: image (package graphics)
> x="A"
> x="ANY"
> 
> The methods are visible to code inside PkgA but others see only the S3 function.
> 
> John
> 
> 
> On Jul 11, 2014, at 11:27 AM, Roger Koenker <rkoenker at illinois.edu> wrote:
> 
>> I've installed R-devel
>> 
>> R Under development (unstable) (2014-07-09 r66111)
>> Platform: x86_64-apple-darwin13.1.0 (64-bit)
>> 
>> and am trying to resolve some problems that I am seeing with my 
>> SparseM package.  In prior versions I explicitly had:
>> 
>> setGeneric("image", function(x, ...) standardGeneric("image"))
>> 
>> and then used setMethod to define a method for the class matrix.csr
>> but my reading of the setGeneric manpage suggests that this call to
>> setGeneric need not, and probably should not have this second 
>> argument, and indeed, need not exist at all, since the generic is
>> automatically created by the setMethod invocation.
>> 
>> However,  what is puzzling to me is that in my new R-devel version
>> none of these options have the intended effect of making "image"
>> a generic and allowing R to dispatch for matrix.csr objects.  When
>> I omit the setGeneric() call, I do get a message at INSTALL time
>> that a generic for image is being created, but then after loading
>> SparseM:
>> 
>>> showMethods(image)
>> Function "image":
>> <not an S4 generic function>
>> 
>> On the command line, I can make this work:
>> 
>>> setGeneric("image")
>> [1] "image"
>>> showMethods(image)
>> Function: image (package graphics)
>> x="ANY"
>> x="matrix.csr"
>> 
>> And -- even more irritating --  if I  require(Matrix)  then the generic
>> is created together with my method and all the Matrix methods.  At 
>> the risk of theorizing without data, I suspect that this has something
>> to do with NAMESPACES, and I have tried to follow the setup for
>> Matrix by having:
>> 
>> importFrom("graphics", image)
>> exportMethods("image")
>> 
>> but clearly I'm still missing some crucial aspect.  Any suggestions
>> would be most welcome.
>> 
>> Roger
>> 
>> 
>> 
>> url:    www.econ.uiuc.edu/~roger            Roger Koenker
>> email    rkoenker at uiuc.edu            Department of Economics
>> vox:     217-333-4558                University of Illinois
>> fax:       217-244-6678                Urbana, IL 61801
>> 
>> ______________________________________________
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>