Christophe Genolini wrote:
>> /I think your question should be more relevant on Rdev./
> ok, I will
>> Personnally I would find stuff like "names", "$", "$<-", or "["
>> useful as these are usual operation with S3 objects.
> Is it possible in S4 to define "$<-" ? If there is a slot name 'a' in
Possible yes, see below. Usual? It implies to the user that this is a
list- or data.frame-like object (where $ is used most commonly). Maybe
your object is not like that? It also seems like a short step from
direct slot access (although it doesn't have to be), which might be
breaking the abstraction layer that object orientation provides. And it
shifts the responsibility for confirming that 'name' is a slot, and
dispatching on different values of 'name' (e.g. for some slots perhaps
one doesn't want to allow access, and then the code inside the '$'
method has to check that), back to the developer (instead of allowing
the method definition and dispatch to do its work). Generally these seem
like backward steps to me.
> setClass("A", representation(x="numeric"))
[1] "A"
> setReplaceMethod("$",
+ signature=signature(
+ x="A",
+ name="ANY",
+ value="ANY"),
+ function(x, name, value) {
+ slot(x, name) <- value
+ x
+ })
[1] "$<-"
> a <- new("A")
> a$x <- 1:5
> a
An object of class "A"
Slot "x":
[1] 1 2 3 4 5
> object 'B', I find (in "S4 in 15 pages more or less")
>
> setGeneric("a<-", function(x, value) standardGeneric("a<-"))
> setReplaceMethod("a", .....
>
> Then we can use
>
> obj <- new("B")
> a(obj)<- 3
>
> But I did not find how to define
>
> obj$a <- 3
>
> Is it possible ? Is it the 'usual' way ?
>
>
> Christophe
>
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