[Rd] False positive note about ambiguous dispatch

[Hervé Pagès]

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
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