Generic Functions

print(1:10)

print <- function(x) "oops"
print(1:10)

rm(print)
print(1:10)

setClass("Foo", "list")
setGeneric("bar", function(x) standardGeneric("bar")) setMethod("bar", 
"Foo", function(x) {}) foo = new("Foo")
bar(foo)

Hi

Many thanks for your explanation. Just another short question. How can 
I make sure that if I greate a new class with functions, that nobody 
can change this functions anymore or as you mentioned overwrite 
unintended this function (setType).

In OOP i.e. in php I have a class and specific functions belongs to 
this class. How can I do the same in R with generic functions? or is 
there another way?

Thanks for your help.

Dominik


PS: I will send questions about S4 to R-devel at r-project.org in future.

-----Urspr?ngliche Nachricht-----
Von: Martin Morgan [mailto:mtmorgan at fhcrc.org]
Gesendet: Sonntag, 24. Februar 2008 17:59
An: Dominik Locher
Cc: r-help at r-project.org
Betreff: Re: [R] Generic Functions

See the 'useAsDefault' argument to setGeneric.

As an aside, if 'setType<-' is meant to be a 'setter' to change the 
value of a slot 'type', then I find the syntax a little redundant -- 
it's use

 > setType(x) <- "foo"

implies that it is already a 'setter' without 'set' at the front. Why 
not just

 > type(x) <- "foo"

(though perhaps 'type' is not such a good name, either)?

As a second aside, if you're writing code that you expect to be used 
with fPortfolio, then having two functions with the same name but 
different signatures or overall goals will confuse your user -- with 
fPortfolio,
setType<- works fine, but then for mysterious reasons (i.e., when your 
package is loaded, with a different definition of setType<-) code that 
worked before no longer works! So I'd either use setType in a way 
consistent with it's use in fPortfolio, or define a new generic for 
your own purposes
(setType<- is not a generic in my version of fPortfolio,

 > packageDescription('fPortfolio')$Version

[1] "260.72"

).

As a third aside, I think questions about S4 probably belong on 
R-devel, as they seem to fall in the realm of 'questions likely to 
prompt discussion unintelligible to non-programmers' (from the R-devel 
mailing list description).

Martin

Dominik Locher wrote:

Hi

I have some problems in defining new generic functions and classes. 
Just have a look at the following example:


require(fPortfolio)

setClass("PROBECLASS",           
  representation(               
    type="character"            
  )                             
)       

isGeneric("setType<-")
#Returns
TRUE

#I would like to define a specific function for class PROBECLASS with 
other arguments than for the generic function "setType" of fPortfolio.
setGeneric("setType<-", function(object, value)
standardGeneric("setType<-"))

#Returns
Fehler in makeGeneric(name, fdef, fdeflt, group = group, valueClass = 
valueClass,  :
  the formal arguments of the generic function for "setType<-" 
(object,
value) differ from those of the non-generic to be used as the default 
(spec,
value)

setReplaceMethod("setType", "PROBECLASS", function(object, value){

  object at type <- value                           
  object

})           

#Example
obj = new("PROBECLASS")
setType(obj) = "test"
obj         


######
If I don't require fPortfolio it works fine. However, is it not 
possible to create two generic functions with the same name but 
different

arguments?

setType for fPortfolio may be differ completely from setType of 
PROBECLASS...
What's the best way to have functions which belongs to an object of a 
specific class? I had a look at the paper "S4 Classes in 15 pages, 
more or less" (feb12, 2003), however, I could not found what I did

wrong...

Any help is highly appreciated. 

Thanks
Dominik