R help - Dec 2004 - setGeneric(rm)

Hi,
We are developing a package using S4 classes. The S4 classes
are wrappers to C++ classes. So S4 classes contain an integer
that is the memory address of one C++ object. If an user
calls the rm() function, the C++ object must be deleted. But our generic
rm() function apparently doesn't work. Here is the code:

# The class
setClass("component", representation(pointer="integer",
"VIRTUAL"))

# The generic method
setGeneric("rm", function(..., list = object, pos = -1, envir =
as.environment(pos), inherits = FALSE)  standardGeneric("rm"))

setMethod("rm", "component", function(list=object, pos,
envir, inherits) {
	warning("object deleted")
	.Call("Rm");i
})

We implemented generic methods for print(), show() and summary() succesfully.

Best,
Marcos Carrero

On Fri, 3 Dec 2004, Marcos Aur??lio Carrero wrote:
> Hi,
> We are developing a package using S4 classes. The S4 classes
> are wrappers to C++ classes. So S4 classes contain an integer
> that is the memory address of one C++ object. If an user
> calls the rm() function, the C++ object must be deleted. But our generic
> rm() function apparently doesn't work. Here is the code:
> 
> # The class
> setClass("component", representation(pointer="integer",
"VIRTUAL"))
> 
> # The generic method
> setGeneric("rm", function(..., list = object, pos = -1, envir =
as.environment(pos), inherits = FALSE)  standardGeneric("rm"))
> 
> setMethod("rm", "component", function(list=object, pos,
envir, inherits) {
> 	warning("object deleted")
> 	.Call("Rm");i
> })
> 
> We implemented generic methods for print(), show() and summary()
succesfully.
> 
I think that you may find reading the code written by Timothy Keitt in the 
rgdal package, especially R/gdal.R, useful. He defines a class with 

representation(handle = 'externalptr')

which I think should be considered as an alternative to integer, because
integer is a vector and externalptr is not - it is an external pointer and
just that. In addition, his code shows how to use .setCollectorFun() as
the collector calling reg.finalizer() in the body of the class definition.
It may well be that you don't need an rm method for your object, I think
reading Tim's code may help you to find a cleaner structure, and 
contribute to solving this question.

Roger
> Best,
> Marcos Carrero
> 
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-- 
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Breiviksveien 40, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 93 93
e-mail: Roger.Bivand at nhh.no

On Fri, 3 Dec 2004, Marcos Carrero wrote:
> We are developing a package using S4 classes. The S4 classes are
> wrappers to C++ classes. So S4 classes contain an integer that is the
> memory address of one C++ object. If an user calls the rm() function,
> the C++ object must be deleted. But our generic rm() function apparently
> doesn't work. Here is the code:
>
> # The class
> setClass("component", representation(pointer="integer",
"VIRTUAL"))
>
> # The generic method
> setGeneric("rm", function(..., list = object, pos = -1,
>                           envir = as.environment(pos),
>                           inherits = FALSE) 
standardGeneric("rm"))
>
> setMethod("rm", "component", function(list=object, pos,
envir, inherits) {
> 	warning("object deleted")
> 	.Call("Rm");i
> })
>
> We implemented generic methods for print(), show() and summary()
succesfully.
The method signatures don't match. Does the warning message
actually display?

BTW, isn't it dangerous to assume a pointer and integer
occupy the same amount of storage?

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SIGSIG -- signature too long (core dumped)