[Rd] UseMethod infelicity
Prof Brian Ripley
ripley at stats.ox.ac.uk
Fri May 19 17:01:21 CEST 2006
If I do
> mycoef <- function(object, ...) UseMethod("coef", object)
Error in mycoef(lm.D9) : no applicable method for "coef"
which is pretty surprising, as coef has a default method.
After a bit of digging, this comes from do_usemethod having
defenv = environment where the generic was defined */
defenv = ENCLOS(env);
so it is assuming that UseMethod() is called within the defining generic
for its first argument. That plainly does not need to be true, e.g.
function (object, ...)
It is clear to me that we need to search for 'generic' and find its
defining environment rather than that of the current caller. It is not
entirely clear where to search from as I think we need to avoid
mycoef <- function(x)
mycoef <- function(x) stop("not this one")
so I used ENCLOS(env).
This adds some overhead, hopefully no more than searching for methods.
BTW, I noticed that R_LookupMethod uses findVar, that is looks for any
object not for functions: that must be another infelicity.
Brian D. Ripley, ripley at stats.ox.ac.uk
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
1 South Parks Road, +44 1865 272866 (PA)
Oxford OX1 3TG, UK Fax: +44 1865 272595
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