Berton Gunter wrote:
Second, in my experiments I couldn't get setReplacementMethod to work:
"bumpIndex<-" <- function(pm, value) {
[EMAIL PROTECTED] <- [EMAIL PROTECTED](value)
pm
}
# I get an error without the next function definition
bumpIndex <- function(pm) [EMAIL PROTECTED]
setReplaceMethod("bumpIndex",
signature=signature(pm="CompletePathMaker",
value="numeric"), bumpIndex)
'bumpIndex' is apparently not a generic function (created by setGeneric)
signature is not an argument to setReplaceMethod
The ... argument to setReplaceMethod must include a function to do the
replacement, which is why you need the bumpIndex function (I agree that this
is not cleanly documented, but it's fairly easy to see since
setReplaceMethod calls setMethod and that requires the function argument).
so I don't see why you expect this to work at all. At the very least,
shouldn't you do what the documentation tells you to? I think that you are
expecting R to work according to your paradigm rather than trying to
understand how it actually works. If you feel that R's paradigm (and/or
documentation) is too awful to bother with, you might consider the R.oo
package, which does OOP an entirely different way.
I have not followed the thread before, but here is an how it could look
like with R.oo:
setConstructorS3("CompletePathMaker", function(index=0) {
extend(Object(), "CompletePathMaker",
index = as.integer(index)
)
})
setMethodS3("increase", "CompletePathMaker", function(this, dindex=+1) {
this$index <- this$index + as.integer(dindex);
# You do not have to return anything here....
})
cpm <- CompletePathMaker()
cpm$index <- 3
increase(cpm, 2)
print(cpm$index)
To add some control of what type of values you can assign to 'index',
you can define a virtual field function set<Field>(), e.g.
setMethodS3("setIndex", "CompletePathMaker", function(this, index) {
if (!is.numeric(index) || length(index) != 1)
stop("Argument 'index' must be a single numeric: ", mode(index));
if (index < 0)
stop("Argument 'index' must be non-negative: ", index);
this$index <- as.integer(index);
# ... or here.
})
cpm$index <- 4
cpm$index <- -3 # Gives an error as wanted!
(Again...) note that setConstructorS3() and setMethodS3() are
conveniency wrappers to define the CompletePathMaker(),
increaseBumpIndex.CompletePathMaker() and
setBumpIndex.CompletePathMaker(). The implementation of references is
taken care of by the special class Object, which also implements support
for virtual fields.
/Henrik
-- Bert Gunter
When I try to load this, I get
arguments in definition changed from (spec) to (object)
arguments in definition changed from (self) to (object)
arguments in definition changed from (self) to (object)
Creating a new generic function for 'bumpIndex<-' in '.GlobalEnv'
Error in conformMethod(signature, mnames, fnames, f) :
In method for function "bumpIndex<-": formal arguments
omitted in the
method definition cannot be in the signature (value = "numeric")
All the errors are triggered by setReplaceMethod. Can anyone help me
interpret them? Or, maybe better, tell me how to debug the
"compilation"?
I leave it to language "experts" to say whether S4 formal
classes and
methods are wise or not in comparison to others. From my
fairly ignorant
perspective, that always seems to be a matter of taste.
There are actually two related issues on that score: first,
whether the
complex of expectation set up by talking about "objects" and "classes"
are met by what R/S does, and second the wisdom of what R/S
does in its
own right.
Cheers,
Bert
--
Ross Boylan wk: (415) 502-4031
530 Parnassus Avenue (Library) rm 115-4 [EMAIL PROTECTED]
Dept of Epidemiology and Biostatistics fax: (415) 476-9856
University of California, San Francisco
San Francisco, CA 94143-0840 hm: (415) 550-1062
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