setGeneric {methods} | R Documentation |
Create a new generic function of the given name, for which formal methods can then be defined.
setGeneric(name, def, group=NULL, valueClass=NULL, where=1, doAssign) setGroupGeneric(name, def, group=NULL, valueClass=NULL, knownMembers, where=1)
name |
The character string name of the generic function. In the simplest and most common case, a function of this name is already defined. The existing function may be non-generic or already a generic (see the details). |
def |
An optional function object, defining the generic. This
argument is usually only needed (and is then required) if there is
no current function of this name. In that case, the formal arguments
and default values for the generic are taken from def . See
also argument useAsDefault .
|
group |
Optionally, a character string giving the group of generic functions to which this function belongs. Methods can be defined for the corresponding group generic, and these will then define methods for this specific generic function, if no method has been explicitly defined for the corresponding signature. See the references for more discussion. |
valueClass |
An optional character string defining the class to asserted to be given to the value returned by this generic function. By default, the generic function can return any object. (At the moment, the assertion supplied in this argument is not enforced or checked.) |
where |
Where to store the resulting initial methods definition, and possibly the generic function; by default, stored into the global environment. |
doAssign |
Should a new generic version of the function be
assigned? The default action depends on whether a generic version
currently exists. If not, one will be assigned to where ,
except that primitive functions in the base package are never turned
into explicit generic functions (they are dispatched from the
internal code in the evaluator).
You can supply doAssign as TRUE to force assigning a
generic function even if one already exists, or as FALSE to
prevent assigning the generic in any case (for example, because you
know one exists on another package). But the rule of not assigning
generics for primitives cannot be overriden by setting
doAssign to TRUE .
|
knownMembers |
(For setGroupGeneric only) The names of functions that are known to be
members of this group. This information is used to reset cached
definitions of the member generics when information about the group
generic is changed.
|
The setGeneric
function is called to initialize a generic
function in an environment (usually the global environment), as
prepartion for defining some methods for that function.
The simplest and most common situation is that name
is already
a function, either an ordinary non-generic function or else a generic
function in another environment. In the second case, essentially all
you will be doing is to make a copy of the existing generic, without
its methods, in the current environment. Only the name
argument will be used. The new generic must agree with the
current one in essentially everything except for the methods defined.
The other simple and common situation is that you already have a
non-generic function (probably in the same place you plan to save the
generic), and now want to turn this function into a generic. In this
case, too, you will most often supply only name
. The existing
function becomes the default method, and the special group
and
valueClass
properties remain unspecified.
The setGroupGeneric
function behaves like setGeneric
except that
it constructs a group generic function, differing in two ways from an
ordinary generic function. First,
this function cannot be called directly, and the body of the function
created will contain a stop call with this information. Second, the
group generic function contains information about the known members of
the group, used to keep the members up to date when the group
definition changes, through changes in the search list or direct
specification of methods, etc.
The setGeneric
function exists for its side effect: saving the
generic function to allow methods to be specified later. It returns name
.
John Chambers
The web page http://www.omegahat.org/RSMethods/index.html is the primary documentation.
The functions in this package emulate the facility for classes and methods described in Programming with Data, (John M. Chambers, Springer, 1998). See this book for further details and examples.
Methods
for a discussion of other functions to
specify and manipulate the methods of generic functions.