2017-09-22 19:04 GMT+02:00 Michael Lawrence <lawrence.mich...@gene.com>: > The %*% function is a primitive. As it says in the documentation under > ?Methods_Details > > Methods may be defined for most primitives, and corresponding > metadata objects will be created to store them. Calls to the > primitive still go directly to the C code, which will sometimes > check for applicable methods. The definition of “sometimes” is > that methods must have been detected for the function in some > package loaded in the session and ‘isS4(x)’ is ‘TRUE’ for the > first argument (or for the second argument, in the case of binary > operators). > > But: >> isS4(x) > [1] FALSE > > I think this behavior is in the interest of performance. It avoids > adding S4 dispatch overhead to e.g. matrix objects.
I see, thanks for the explanation. > In general, it's best to define an S4 class when using S4 dispatch, > but it sounds like you're stuck using some legacy S3 objects. In that > case, one would normally define an S3 method for `%*%()` that > delegates to a custom non-primitive generic, perhaps "matmult" in this > case. But since %*% is not an S3 generic, that's not an option. > > It would help to hear more about the context of the problem. This is a problem that Edzer Pebesma and I are facing in our packages units and errors respectively (you can find both on CRAN). They are designed in a similar way: units or errors are attached to numeric vectors as an attribute of an S3 class, and Ops, Math and Summary are redefined to cope with such units/errors. Then Edzer found that the %*% operator silently drops the attributes, so we were trying, without success, to set a method for our respective S3 classes to at least show a warning stating that the units/errors are being dropped. Ours are perfect use cases for S3 classes, and it would be a pitty if we have to switch everything to S4 just to show a warning. Clearly overkilling. Isn't there another way? Iñaki ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
