Overriding S4 methods in an installed package

Seth Falcon wrote:

Allen McIntosh <mcintosh at research.telcordia.com> writes:

Is it possible to override S4 methods in an installed package?
The naive
library("pkg")
setMethod("foo", signature(obj = "bar"),
        function(obj , x, y) { new definition }
	, where="package:pkg")
results in the error
Error in setMethod("foo", signature(obj = "bar"), function(obj,  :
        the environment "pkg" is locked; cannot assign methods for function "foo"

If foo is a generic that you are calling directly, then you can
probably define it in the global environment (omit the where arg) and
test it that way.

OTOH, if foo is used by pkg internally, then it will be much easier to
simply edit the source for pkg, reinstall and test.  If you find and
fix a bug, most package maintainers will be quite happy to integrate
your fix.

Thanks for the suggestion.  Unfortunately, foo() uses internal 
functions.  When foo() is defined in the global environment, these are 
not visible.

I think you can set the environment of your method to see the package 
internals.  Those internals won't see your method, though.

To do this, you'd do something like

newfoo <- function(obj , x, y) { new definition }
environment(newfoo) <- environment(foo) # or some other function from 
the package

setMethod("foo", signature(obj = "bar"),
        newfoo)
I was hoping to avoid recompiling and installing under Windows.  Looks 
like I may not have a choice.

This is getting easier:  we're down to a single install, as long as you 
don't need all possible formats of man pages.

Duncan Murdoch
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Overriding S4 methods in an installed package

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