Re: [Rd] False positive note about ambiguous dispatch

From: Hervé Pagès <hpages_at_fhcrc.org>
Date: Tue, 02 Oct 2012 14:24:13 -0700

Thanks you.

H.

On 10/02/2012 01:56 PM, John Chambers wrote:
> 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.
>>
>>

-- 
Hervé Pagès

Program in Computational Biology
Division of Public Health Sciences
Fred Hutchinson Cancer Research Center
1100 Fairview Ave. N, M1-B514
P.O. Box 19024
Seattle, WA 98109-1024

E-mail: hpages_at_fhcrc.org
Phone:  (206) 667-5791
Fax:    (206) 667-1319

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