From jmc at r-project.org  Tue Oct  2 22:56:23 2012
From: jmc at r-project.org (John Chambers)
Date: Tue, 02 Oct 2012 13:56:23 -0700
Subject: [Rd] False positive note about ambiguous dispatch
In-Reply-To: <506A1719.2010904@fhcrc.org>
References: <506A1719.2010904@fhcrc.org>
Message-ID: <506B54F7.20803@r-project.org>

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, Herv? Pag?s 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.
>
>



[Rd] False positive note about ambiguous dispatch
John Chambers