The advantage of .Primitive over .Internal
  functions is the potential efficiency of argument passing, and that
  positional matching can be used where desirable, e.g.in
  switch. For more details, see the ‘R Internals
    Manual’.
All primitive functions are in the base namespace.
This function is almost never used: `name` or, more carefully,
  get(name, envir = baseenv()) work equally well and do
  not depend on knowing which functions are primitive (which does change
  as R evolves).