[Rd] namespace S3 and S4 generic imports cannot both be satisfied:

Martin Morgan mtmorgan at fhcrc.org
Sun Dec 9 00:05:37 CET 2012

PkgA wishes to write a method for 'unique' on S4 class 'A'. ?Methods indicates 
that one should


   unique.A <- function(x, incomparables=FALSE, ...) {}
   setMethod(unique, "A", unique.A)

Both S3 and S4 methods need to be exported in the NAMESPACE

   S3method(unique, A)

PkgB introduces a new class and method

   unique.B <- function(x, incomparables=FALSE, ...) {}
   setMethod(unique, "B", unique.B)

and in the NAMESPACE has

   importFrom(PkgA, unique)
   S3method(unique, B)

Unfortuantely, R CMD check says that

* checking whether package 'PkgB' can be installed ... WARNING
Found the following significant warnings:
   Warning: found an S4 version of 'unique' so it has not been imported correctly
See '/home/mtmorgan/tmp/PkgB.Rcheck/00install.out' for details.

This is from (svn r61253) R-devel/src/library/base/R/namespace.R:1339, where the 
code finds the S4 generic, but not the S3 generic. Obviously the namespace 
cannot have both the S3 and S4 symbols defined, but this seems to be required? A 
workaround might extend the check to include getGeneric(genname)@default.

This scenario is reproducible in the attached tarball

   tar xzf PkgAB.tar.gz
   R CMD check PkgB

Martin Morgan
Computational Biology / Fred Hutchinson Cancer Research Center
1100 Fairview Ave. N.
PO Box 19024 Seattle, WA 98109

Location: Arnold Building M1 B861
Phone: (206) 667-2793
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