With the help of Martin Morgan here is the solution for the above question.
First create VIRTUAL class with all the test for children classes:
setClass("TESTS", validity=function(object) {
cat("Validity here:", class(object), "\n")
TRUE
})
.simple <- function(object) {
cat("No validity -", class(object), "\n")
TRUE
}
setClass("A", representation(a="numeric", n="integer"),
validity=.simple)
setClass("B", representation("A", b="numeric"),
validity=.simple)
setClass("C", representation("B", c="numeric"),
validity=.simple)
Set each children to inherit from TESTS class:
setIs("B", "TESTS")
setIs("C", "TESTS")
Now we have exactly what we wanted, validity tests are executed only once:
res <- new("B", b=1)
Validity here: B
No validity - A
No validity - B
res <- new("C", c=1)
No validity - A
Validity here: C
No validity - B
No validity - C
The order in which validity is called above is somewhat counter intuitive.
For class "C" complete hierarchy is this:
superClassDepth(getClass("C"))$label
[1] "B" "TESTS" "A" "TESTS" "TESTS"
so if validity would start bottomup then TEST should be the first to
follow. And vector of unique superclasses would be
c("B", "A", "TEST").
Instead validity uses the vector of unique labels constructed *TOPDOWN* :
getAllSuperClasses(getClass("C"))
[1] "B" "TESTS" "A"
Apparently this is an inconsistency in implementation, isn't it?
Vitalie.
On Mon, 17 Aug 2009 20:06:44 +0200, Vitalie S. <vitosm...@rambler.ru>
wrote:
Dear Developers,
In current implementation of validity method, objects are first coerced
to superclass (slots are striped). Thus, it is not possible to write
validity method which would perform some checks on children slots.
Say, I want to check if number of slots in a class is equal to "n":
setClass("A", representation(a="numeric", n="integer"),
prototype=list(a=12, n=1L),
validity=function(object){
if(length(slotNames(object))!=obj...@n+1) paste("Number of
slots must be ", obj...@n)
else TRUE
})
setClass("B", representation(b="numeric"), contains="A",
prototype=list(a=12, b=14, n=2L))
new("B", a=11, b=33)
Error in validObject(.Object) :
invalid class "B" object: Number of slots must be 2
Error, because an object of class "A" is passed to validObject with one
slot "b" removed and n=2.
Is were a work around for this, or I am just doomed to write the same
validity method for each children class?
Many thanks,
Vitalie.
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