[Bioc-devel] testing class and length of function args

it's slightly annoying to write

foo <- function(x) {
  if ( ! is.numeric(x) ) stop("x should be numeric")
  if ( ! length(x) == 2 ) stop("x should be length 2")
  c(x[2], x[1])
}

i wonder if we could have some core functions that test the class and
the length in one and give the appropriate stop message.

maybe this exists already

-Mike