From hpages at fhcrc.org  Tue Oct  2 00:20:09 2012
From: hpages at fhcrc.org (=?windows-1252?Q?Herv=E9_Pag=E8s?=)
Date: Mon, 01 Oct 2012 15:20:09 -0700
Subject: [Rd] False positive note about ambiguous dispatch
Message-ID: <506A1719.2010904@fhcrc.org>

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.


-- 
Herv? Pag?s

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



[Rd] False positive note about ambiguous dispatch
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