Extract or replace the contents of a slot in a object with a formal (S4) class structure.
object@name
object@name <- valueAn object from a formally defined (S4) class.
The character-string name of the slot, quoted or
      not.  Must be the name of a slot in the definition of the class
      of object.
A replacement value for the slot, which must be from a
      class compatible with the class defined for this slot in the
      definition of the class of  object.
The current contents of the slot.
These operators support the formal classes of package methods,
  and are enabled only when package methods is loaded (as per
  default).  See slot for further details, in particular
  for the differences between slot() and the @ operator.
It is checked that object is an S4 object (see
  isS4), and it is an error to attempt to use @ on
  any other object.  (There is an exception for name .Data for
  internal use only.)  The replacement operator checks that the slot
  already exists on the object (which it should if the object is really
  from the class it claims to be).
These are internal generic operators: see InternalMethods.