Quoting Peng Yu <pengyu...@gmail.com>:
In the following code, 'multiply' doesn't multiply a...@x by 2. I'm
wondering how to define a method that can change the slot of a class.
$ Rscript setGeneric.R
setClass(
+ Class='A',
+ representation=representation(
+ x='numeric'
+ )
+ )
[1] "A"
setMethod(
+ f='initialize',
+ signature='A',
+ definition=function(.Object,x){
+ cat("~~~ A: initializator ~~~\n")
+ .Object<-callNextMethod(.Object,x=x)
+ return(.Object)
+ }
+ )
[1] "initialize"
setGeneric(
+ name='multiply',
+ def=function(object){
+ standardGeneric('multiply')
+ }
+ )
[1] "multiply"
setMethod(
+ f='multiply',
+ signature='A',
+ definition=function(object){
+ obj...@x=object@x*2
+ }
+ )
Remember that R has 'copy on change' semantics, so obj...@x =
obj...@x^2 creates a (seemingly -- we don't 'know' what is going on
underneath) new instance of object, and assigns the value of
obj...@x^2 to its 'x' slot. So the original 'object' is unchanged. If
you return object,
setMethod(multiply, "A", function(object) {
obj...@x = obj...@x^2
object
})
then
a = multiply(a)
will update the value of a. It is worth noting the implied copying
going on here, and the implications for performance.
R.oo and proto will provide a more familiar paradigm (though perhaps
no less copying, in general).
Martin
[1] "multiply"
a=new(Class='A',x=10)
~~~ A: initializator ~~~
multiply(a)
print(a...@x)
[1] 10
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