>>>> "JC" == John Chambers <j...@r-project.org>
>>>> on Fri, 06 Mar 2009 14:12:00 -0800
JC> Some modifications have been committed for the r-devel
JC> version today
JC> that modify (essentially, correct a bug in) the communication
JC> of objects
JC> to an S3 method from an S4 class that extends the S3 class.
JC>
JC> This is one of a sequence of changes designed to make S4
JC> classes work
JC> more generally and consistently with S3 methods and classes.
JC>
JC> In 2.8.0, support was provided for S4 classes that extend
JC> S3 classes,
JC> partly by making S3 method dispatch recognize the inheritance.
JC>
JC> The catch was that the S3 method would get the S4 object.
JC> Two problems
JC> with that:
JC>
JC> 1. The S3 method would fail if it tried to use the S3 class
JC> information
JC> directly, since the class attribute was the S4 class.
JC>
JC> 2. More seriously, if the method used the object, modified
JC> it and
JC> returned the result, it had a good chance of returning an
JC> invalid object
JC> seeming to come from the S4 class.
JC>
JC> The modification to deal with this now delivers to the S3
JC> method the
JC> inherited S3 object. (This turned out to be somewhat harder
JC> than the
JC> original change, since it impacts several pieces of internal
JC> code.) A
JC> revision of the function asS4() deals with similar concerns--see
JC> the
JC> documentation.
JC>
JC> The change does not affect default methods. It would be
JC> tempting to
JC> convert S4 objects for those, but some S3 generics attempt to
JC> deal with
JC> S4 objects, e.g., str(). A change to the primitives that
JC> dispatch
JC> methods is more plausible, but for the moment all that was
JC> added was
JC> more explicit error messages if a non-vector S4 object is
JC> supplied.
JC>
JC> For more information see the section on inheriting from
JC> non-S4 classes
JC> in the documentation ?Classes.
JC>
JC> It would be helpful if package maintainers would check this
JC> and previous
JC> changes by running their code against the r-devel version of
JC> R, before
JC> that becomes 2.9.0. Please report any new errors (provided,
JC> of course,
JC> that the same code works with 2.8.1).
JC>
JC> John
JC>
Dear John,
it seems that S3 methods for an S4 class which extents a
matrix cannot be defined as it used to be the case in 2.8.1.
For example
## code
setClass("aTest",
representation(.Data = "matrix",
comment = "character"))
c1 <- new("aTest", .Data = matrix(1:4, ncol = 2), comment = "aTest")
# it seems that it is no longer possible to define an S3
# method for the class aTest
print.aTest <- function(x, ...)
{
cat("\n", x...@comment, "\n")
print(getDataPart(x))
}
print.aTest(c1)
print(c1) # works in 2.8.1
# another example could be
as.matrix.aTest <- function(x, ...) getDataPart(x)
as.matrix.aTest(c1)
as.matrix(c1) # works in 2.8.1
## end code
Is this the expected behavior?
Best regards,
Yohan
--
PhD student
Swiss Federal Institute of Technology
Zurich
www.ethz.ch
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