I discovered the following behavior when source'ing the same file
repeatedly as I edited it. My generic stopped acting like a generic. I
can't tell from the docs what, if any, behavior is expected in this
case. R 2.4.0
> foo <- function(object) 3
> isGeneric("foo")
[1] FALSE> setMethod("foo", "matrix", function(object) 4)
Creating a new generic function for "foo" in ".GlobalEnv"
[1] "foo"> foo(0)
[1] 3> foo(matrix(0))
[1] 4> isGeneric("foo")
[1] TRUE
# The next step is where things start to go astray> foo <- function(object) 2
> isGeneric("foo")
[1] TRUE> setMethod("foo", "matrix", function(object) 40)
[1] "foo"> foo(0)
[1] 2
# isGeneric is TRUE, but method lookup no longer works
# I think the cause is that the function foo that used
# to do the dispatch has been overwritten by my plain old
# function that returns 2.> foo(matrix(0))
[1] 2> removeGeneric("foo")
[1] FALSE
Warning message:
generic function "foo" not found for removal in:
removeGeneric("foo") > isGeneric("foo")
[1] TRUE
My mental model and R's diverged at the point I overwrote foo with a
regular function (foo <- function(object) 2). At this point I thought R
would know that the function was no longer generic, and then would
rebuild the generic at the next setMethod. Instead, R thought the
function remain generic, and so did not rebuild it at the next
setMethod.
If I had practiced the recommended style, I would have done
foo<-function(object) 2
setGeneric("foo")
and all would have been well. So that's what I'll do.
I thought I'd report this in case others run into it, or somebody
considers this a matter that calls for documentation or R behavior
changes.
--
Ross Boylan wk: (415) 514-8146
185 Berry St #5700 ross at biostat.ucsf.edu
Dept of Epidemiology and Biostatistics fax: (415) 514-8150
University of California, San Francisco
San Francisco, CA 94107-1739 hm: (415) 550-1062
