[Rd] False positive note about ambiguous dispatch
John Chambers
jmc at r-project.org
Tue Oct 2 22:56:23 CEST 2012
The as() function does some non-standard stuff, and it appears in this
example to set up methods for coerce() in a way that fools the
disambiguation code (which is newer than the as() code, I think).
Pending a rewrite of as() (not imminent) the Note has been deactivated
for the coerce() generic. (rev 60859)
Thanks for the catch.
John
On 10/1/12 3:20 PM, Hervé Pagès wrote:
> Hi,
>
> In the situation below the note issued by the dispatch algo doesn't
> seem right:
>
> setClass("A", representation(stuff="complex"))
> setAs("ANY", "A", function(from) new("A", stuff=as.complex(from)))
>
> > as(6, "A")
> An object of class "A"
> Slot "stuff":
> [1] 6+0i
>
> > as(6L, "A")
> Note: Method with signature ‘numeric#A’ chosen for function ‘coerce’,
> target signature ‘integer#A’.
> "ANY#A" would also be valid
> An object of class "A"
> Slot "stuff":
> [1] 6+0i
>
> First thing is that the note is in contradiction with the output of
> selectMethod (seems like it's the method with signature "ANY#A" that
> was chosen, not the method with signature "numeric#A"):
>
> > selectMethod("coerce", c("integer", "A"))
> Method Definition:
>
> function (from, to = "A", strict = TRUE)
> new("A", stuff = as.complex(from))
>
> Signatures:
> from to
> target "integer" "A"
> defined "ANY" "A"
>
> Second, and more importantly, there is no need for a note in the first
> place because there is no ambiguity at all (the method for "numeric#A"
> itself is inherited from "ANY#A"):
>
> > selectMethod("coerce", c("numeric", "A"))
> Method Definition:
>
> function (from, to = "A", strict = TRUE)
> new("A", stuff = as.complex(from))
>
> Signatures:
> from to
> target "numeric" "A"
> defined "ANY" "A"
>
> showMethod gives me an overview of the situation (which is much
> simpler/cleaner than what the note is suggesting):
>
> > showMethods("coerce")
> Function: coerce (package methods)
> from="ANY", to="A"
> ...
> from="integer", to="A"
> (inherited from: from="ANY", to="A")
> ...
> from="numeric", to="A"
> (inherited from: from="ANY", to="A")
>
> Finally, if I switch the order (i.e. if I do 'as(6L, "A")' before
> 'as(6, "A")'), I don't get the note.
>
> I get this with R 2.15.1 and a recent R devel (2012-09-22 r60777).
> It looks like a regression because I was not able to reproduce with
> R <= 2.14.
>
> Thanks,
> H.
>
>
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