Loading an S4 object from a file without first loading the library sometimes (?,
the example below and actual example involves a virtual base class and the show
generic) leads to incorrect dispatch (to the base class method).
The attached package reproduces the problem. It has
setClass("A")
setClass("B", contains="A")
setMethod("show", "A", function(object) cat("A\n"))
setMethod("show", "B", function(object) cat("B\n"))
with NAMESPACE
import(methods)
exportClasses(A, B)
exportMethods(show)
This creates the object and illustrated expected behavior
~/tmp$ R --vanilla --slave -e "library(PkgA); b = new('B'); save(b,
file='b.Rda'); b"
B
Loading PkgA before the object leads to correct dispatch
~/tmp$ R --vanilla --slave -e "library(PkgA); load(file='b.Rda'); b"
B
but loading the object without first loading PkgA leads to dispatch to
show,A-method.
~/tmp$ R --vanilla --slave -e "load(file='b.Rda'); b"
Loading required package: PkgA
A
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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