S3 method dispatch overhead.md

The overhead of method dispatching can be noticable, particularly if done on small objects and it adds up if doing many many times. For instance,

> add <- function(a,b) UseMethod("add")
> add.integer <- function(a,b) a+b

gives with method dispatching:

> system.time({ for (kk in 1:10e6) add(1L, 2L) })
  user  system elapsed
 35.43    0.05   35.70

and without:

> system.time({ for (kk in 1:10e6) add.integer(1L, 2L) })
  user  system elapsed
  7.80    0.02    7.86