R devel - Apr 2008 - S3 method despatch (changed between 2.6.2 and 2.7.0 RC?)

Dear developers:

I have observed a change in the behaviour of S3 method despatch (as I
guess related to namespaces) between 2.6.2 and yesterday's 2.7.0 RC and
would be grateful if you could comment on that:

the 'Axis' function in the 'graphics' namespace calls
UseMethod("Axis",x), internally to despatch on the S3 Axis method
depending on the type of the argument. Both 2.6.2 and 2.7.0 define the
following Axis.* methods in 'graphics': Axis.Date, Axis.POSIXct
Axis.POSIXlt and Axis.default. Now, if one defines an Axis.MyClass
outside of the 'graphics' namespace, it is called automatically by 2.6.2
on objects of MyClass, i.e. R would search for further method definition
outside of the graphics namespace. Looks like this behaviour has changed
in 2.7.0 so that UseMethod called in a given namesspace (graphics) does
not despatch on methods defined in another namespace (global or another
package) as the example below shows.

Have I done something wrong?

Is it an intended behaviour, any idea how to go around it?

Thanks,
Oleg

PS: The difference in the code below is that 2.6.2 calls Axis.MyClass in
plot.default (and thus prints the message), while 2.7.0 does not.

x = 1:5
class(x) = c("MyClass",class(x))
Axis.MyClass = function (x, at, ..., side, labels=TRUE) {
    print("running Axis.MyClass")
    axis(side, at=if(!missing(x)) x else at, labels=labels, ...)
}
methods("Axis")
plot(x, 1:5)

== >>> Output from 2.6.2 RC (2008-02-08)
======================================> methods("Axis")
[1] Axis.Date*    Axis.MyClass  Axis.POSIXct* Axis.POSIXlt*
Axis.default*

   Non-visible functions are asterisked
> plot(x, 1:5)
[1] "running Axis.MyClass"
>
> sessionInfo()
R version 2.6.2 (2008-02-08)
x86_64-unknown-linux-gnu

locale:
LC_CTYPE=en_GB.UTF-8;LC_NUMERIC=C;LC_TIME=en_GB.UTF-8;LC_COLLATE=C;LC_MO
NETARY=en_GB.UTF-8;LC_MESSAGES=en_GB.UTF-8;LC_PAPER=en_GB.UTF-8;LC_NAMEC;LC_ADDRESS=C;LC_TELEPHONE=C;LC_MEASUREMENT=en_GB.UTF-8;LC_IDENTIFICATI
ON=C

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base

loaded via a namespace (and not attached):
[1] rcompgen_0.1-17 tools_2.6.2

== >>> Output from 2.7.0 RC (2008-04-20 r45403)
===============================> methods("Axis")
[1] Axis.Date*    Axis.MyClass  Axis.POSIXct* Axis.POSIXlt*
Axis.default*

   Non-visible functions are asterisked
> plot(x, 1:5)
>
> sessionInfo()
R version 2.7.0 RC (2008-04-20 r45403)
x86_64-unknown-linux-gnu

locale:
LC_CTYPE=en_GB.UTF-8;LC_NUMERIC=C;LC_TIME=en_GB.UTF-8;LC_COLLATE=C;LC_MO
NETARY=C;LC_MESSAGES=en_GB.UTF-8;LC_PAPER=en_GB.UTF-8;LC_NAME=C;LC_ADDRE
SS=C;LC_TELEPHONE=C;LC_MEASUREMENT=en_GB.UTF-8;LC_IDENTIFICATION=C

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base

loaded via a namespace (and not attached):
[1] tools_2.7.0


Dr Oleg Sklyar
Technology Group
Man Investments Ltd
+44 (0)20 7144 3803
osklyar at maninvestments.com


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