getMethod and selectMethod return the method; the functions
existsMethod and hasMethod test for its existence. In both
cases the first function only gets direct definitions and the second
uses inheritance. In all cases, the search is in the generic function itself or in
the package/environment specified by argument where. The function findMethod returns the package(s) in the search
list (or in the packages specified by the where argument) that
contain a method for this function and signature.
getMethod(f, signature=character(), where, optional = FALSE, mlist, fdef)
existsMethod(f, signature = character(), where)
findMethod(f, signature, where)
selectMethod(f, signature, optional = FALSE, useInherited =, mlist = , fdef = , verbose = , doCache = )
hasMethod(f, signature=character(), where)f. See the details below.
selectMethod does not find a valid method
an error is generated, unless this argument is TRUE. In that
case, the value returned is NULL if no method matches.getMethod and selectMethod for
internal use. Avoid
these: some will work as expected and others will not, and none of them is required for normal use of the functions.
selectMethod or getMethod returns the selected method, if
one is found.
(This class extends function, so you can use the result
directly as a function if that is what you want.)
Otherwise an error is thrown if optional is FALSE and NULL is returned if
optional is TRUE.The returned method object is a
MethodDefinition object, except that the default method for a primitive function is required to be the primitive itself.
Note therefore that the only reliable test that the search failed is is.null().signature argument specifies classes, corresponding to formal arguments of the generic function; to be precise, to the signature slot of the generic function object.
The argument may be a vector of strings identifying
classes, and may be named or not. Names, if supplied, match the
names of those formal arguments included in the signature of the
generic. That signature is normally all the arguments except
.... However, generic functions can be specified with only a
subset of the arguments permitted, or with the signature taking
the arguments in a different order. It's a good idea to name the arguments in the signature to avoid
confusion, if you're dealing with a generic that does something
special with its signature. In any case, the elements of the
signature are matched to the formal signature by the same rules
used in matching arguments in function calls (see
match.call).
The strings in the signature may be class names, "missing"
or "ANY". See Methods for the meaning of these in
method selection. Arguments not supplied in the signature
implicitly correspond to class "ANY"; in particular, giving
an empty signature means to look for the default method.
A call to getMethod returns the method for a particular
function and signature. As with other get functions,
argument where controls where the function looks (by default
anywhere in the search list) and argument optional controls
whether the function returns NULL or generates an error if
the method is not found. The search for the method makes no use of
inheritance.
The function selectMethod also looks for a method given the
function and signature, but makes full use of the method dispatch
mechanism; i.e., inherited methods and group generics are taken into
account just as they would be in dispatching a method for the
corresponding signature, with the one exception that conditional
inheritance is not used. Like getMethod, selectMethod
returns NULL or generates an error if
the method is not found, depending on the argument optional.
The functions existsMethod and hasMethod return
TRUE or FALSE according to whether a method is found,
the first corresponding to getMethod (no inheritance) and the
second to selectMethod.
Chambers, John M. (1998) Programming with Data Springer (For the original S4 version.)
Methods for the details of method
selection; GenericFunctions for other functions
manipulating methods and generic function objects;
MethodDefinition for the class that represents
method definitions.setGeneric("testFun", function(x)standardGeneric("testFun"))
setMethod("testFun", "numeric", function(x)x+1)
hasMethod("testFun", "numeric")
## Not run: [1] TRUE
hasMethod("testFun", "integer") #inherited
## Not run: [1] TRUE
existsMethod("testFun", "integer")
## Not run: [1] FALSE
hasMethod("testFun") # default method
## Not run: [1] FALSE
hasMethod("testFun", "ANY")
## Not run: [1] FALSE
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