NextMethod() quirks: It's not a regular function - don't pass arguments! about wishlist-for-r

[alanocallaghan]

NextMethod is a super weird function in general. I've discovered (through some hacking) that you can use it in place of UseMethod to define default behaviour for all subclasses, as long as the methods are not tagged as s3 methods.

Thanks for this exploration of the arguments, it has confused me many times

[HenrikBengtsson]

Looking at the R source itself, we see that NextMethod() is called in several different ways, e.g.

src/library/base/R/datetime.R:        NextMethod(.Generic)
src/library/base/R/datetime.R:            return(structure(NextMethod(.Generic),
src/library/base/R/datetime.R:            return(structure(NextMethod(.Generic),
src/library/base/R/datetime.R:            structure(NextMethod(.Generic), units=u1, class = "difftime")
src/library/base/R/datetime.R:            structure(NextMethod(.Generic), units = "secs", class = "difftime")
src/library/base/R/datetime.R:               .difftime(NextMethod(), units)
src/library/base/R/datetime.R:    y <- NextMethod()
src/library/base/R/datetime.R:    NextMethod("duplicated", x)
src/library/base/demo/is.things.R:    } else NextMethod("print", ...)
src/library/parallel/R/snow.R:    v <- NextMethod()

This suggests that R core themselves don't have a standard way of using NextMethod() - maybe there's room for improvement to both the code and the docs?