Set operation generics

Would anyone be interested in reviewing a patch to make the set
operations (union, intersect, setdiff, setequal, is.element) generic?

S3 generics, S4 generics, or primitives?

Note that all those things heavily rely on match() behind the scene.
If match() itself was an S4 generic (or a primitive like c() and [)
then union(), intersect(), setdiff(), is.element() could be defined
with something like:


  union <- function(x, y)
  {
    xy <- c(x, y)
    sm <- match(xy, xy)
    xy[sm == seq_along(sm)]
  }

  intersect <- function(x, y)
  {
    sm <- match(x, x)
    x <- x[sm == seq_along(sm)]
    m <- match(x, y)
    x[!is.na(m)]
  }

  setequal <- function(x, y)
  {
    !(anyNA(match(x, y)) || anyNA(match(x, y)))
  }

For the record, match(), union(), intersect(), and setdiff() are S4
generics in the BiocGenerics package. But there is no doubt it would
be a better/cleaner situation if base::match() itself was an S4 generic
or primitive.