On 02/20/2013 02:19 AM, Romain Fenouil wrote:
Dear members,
please excuse me for eventual mistake in posting my first message on this
list.
I am actually glad to read these very interesting questions and answers
because I have been facing a related situation for the last 2 days. I am
writing a R package that is using some of the interesting functions offered
by Dr. Morgan's 'ShortRead' library.
I have a C++/Java background and only used R as a scripting language until
now.
I am now writing my first class with R and everything seems fine until I
tried to define a function (accessor) named 'chromosome' for it.
Indeed this function name is already used in ShortRead library as an
accessor to the corresponding slot.
My others accessors are usually defined like this :
# Getter
setGeneric(name="pairedEnds", def=function(object, ...)
{standardGeneric("pairedEnds")});
setMethod( f="pairedEnds",
signature="myClass",
definition=function(object, ...) {return(slot(object,
"pairedEnds"))});
# Setter
setGeneric(name="pairedEnds<-", def=function(object, value)
{standardGeneric("pairedEnds<-")});
setReplaceMethod( f="pairedEnds",
signature="AlignedData",
definition=function(object, value) {object@pairedEnds<-value;
validObject(object); return(object);});
However, I realized that when I tried to do the same with the 'chromosome'
function, calling setGeneric overrides the previous 'definition' (the
'ShortRead' one) and if I understand correctly, masked it. The consequence
is that I cannot use chromosome anymore on a 'ShortRead' object
('alignedRead').
actually, the original generic and its methods are still available with
ShortRead::chromosome
I think I understood that we can only call setGeneric once per function
name. By the way, if I ommit my setGeneric and only use the setMethod in my
package, it seems to work correctly, probably basing it on the setGeneric
call from the ShortRead library.
My questions are :
1. Is my last statement correct ?
maybe; you should have in your DESCRIPTION file
Imports: ShortRead
and in your NAMESPACE file
importFrom(ShortRead, chromosome)
2. How to define a function with the same name as one previously existing in
another package ? How to avoid conflicts in case we load these two packages
at the same time ?
inside your package, you're free to do what you like. If you don't want to
re-use the ShortRead::chromosome generic, then don't importFrom(ShortRead,
chromosome)
3. In order to avoid several calls to setGeneric, I have been thinking about
a conditional use of setGeneric 'if(!is.generic(myFunc)) setGeneric(myFunc)'
but it seems tricky and I have never seen such use, I guess this would be
problematic...
this used to be an idiom when there was no NAMESPACE, but inside your package
you know what generics are defined (you've imported them explicitly) so no need
to test whether they exist or not.
4. Is this phenomenon happening because I'm doing this in the global
environment (Testing) ? Would it be transparent when in the package
Namespace ?
Yes to some extent there are fewer conflicts -- inside your package -- when
using a NAMESPACE.
This method dispatching is very disappointing to me... I believe that these
questions come from my general misunderstanding of how R OOP is designed and
I would be glad to find a reference document for S4.
I would guess that what you want to do is reuse the ShortRead generic, not
create a new one, and add your method to it
DESCRIPTION:
Imports: ShortRead
NAMESPACE:
importFrom(ShortRead, chromosome)
exportMethods(chromosome)
R/somewhere.R
setMethod(chromosome, "MyClass", function(object, ...) {
## implementation
})
Hope that helps, and good luck with your package.
Martin
Thank you very much for your help.
Romain Fenouil.
--
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http://r.789695.n4.nabble.com/2-setGeneric-s-same-name-different-method-signatures-tp4658570p4659139.html
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