| GenericFunctions {methods} | R Documentation |
The functions documented here manage collections of methods associated with a generic function, as well as providing information about the generic functions themselves.
isGeneric(f, where, fdef, getName = FALSE) isGroup(f, where, fdef) removeGeneric(f, where) dumpMethod(f, signature, file, where, def) findFunction(f, generic = TRUE, where = topenv(parent.frame())) dumpMethods(f, file, signature, methods, where) signature(...) removeMethods(f, where = topenv(parent.frame()), all = TRUE) setReplaceMethod(f, ..., where = topenv(parent.frame())) getGenerics(where, searchForm = FALSE) allGenerics(where, searchForm = FALSE) callGeneric(...)
f |
The character string naming the function. |
where |
The environment, namespace, or search-list position from which to search for objects. By default, start at the top-level environment of the calling function, typically the global environment (i.e., use the search list), or the namespace of a package from which the call came. It is important to supply this argument when calling any of these functions indirectly. With package namespaces, the default is likely to be wrong in such calls. |
signature |
The class signature of the relevant method. A
signature is a named or unnamed vector of character strings. If
named, the names must be formal argument names for the generic
function. If signature is unnamed, the default is to use
the first length(signature) formal arguments of the
function. |
file |
The file on which to dump method definitions. |
def |
The function object defining the method; if omitted, the current method definition corresponding to the signature. |
... |
Named or unnamed arguments to form a signature. |
generic |
In testing or finding functions, should generic
functions be included. Supply as FALSE to get only
non-generic functions. |
fdef |
Optional, the generic function definition.
Usually omitted in calls to isGeneric |
getName |
If TRUE, isGeneric returns the name of
the generic. By default, it returns TRUE. |
methods |
The methods object containing the methods to be dumped. By default,
the methods defined for this generic (optionally on the specified
where location).
|
all |
in removeMethods, logical indicating if all
(default) or only the first method found should be removed. |
searchForm |
In getGenerics, if TRUE, the
package slot of the returned result is in the form used
by search(), otherwise as the simple package name (e.g,
"package:base" vs "base").
|
isGeneric:f, and if so, is it a generic?
The getName argument allows a function to find the name
from a function definition. If it is TRUE then the name of
the generic is returned, or FALSE if this is not a generic
function definition.
The behavior of isGeneric and getGeneric for
primitive functions is slightly different. These functions don't
exist as formal function objects (for efficiency and historical
reasons), regardless of whether methods have been defined for
them. A call to isGeneric tells you whether methods have
been defined for this primitive function, anywhere in the current
search list, or in the specified position where. In
contrast, a call to getGeneric will return what the
generic for that function would be, even if no methods have been
currently defined for it.
removeGeneric, removeMethods:removeGeneric removes the function
itself; removeMethods restores the non-generic function
which was the default method. If there was no default method,
removeMethods leaves a generic function with no methods.
standardGeneric:f. It is an error to call
standardGeneric anywhere except in the body of the
corresponding generic function.
Note that standardGeneric is a primitive function in
the base package
for efficiency
reasons, but rather documented here where it belongs naturally.
dumpMethod:findFunction:name exists. The returned value is always a
list, use the first element to access the first visible version
of the function. See the example.
NOTE: Use this rather than find with
mode="function", which is not as meaningful, and has a few
subtle bugs from its use of regular expressions. Also,
findFunction works correctly in the code for a package
when attaching the package via a call to library.
dumpMethods:signature:getGenerics:where; this
argument can be an environment or an index into the search
list. By default, the whole search list is used.
The methods definitions are stored with
package qualifiers; for example, methods for function
"initialize" might refer to two different functions
of that name, on different packages. The package names
corresponding to the method list object are contained in the
slot package of the returned object. The form of
the returned name can be plain (e.g., "base"), or in
the form used in the search list ("package:base")
according to the value of searchForm
callGeneric:callGeneric, the arguments to the current call are passed
down; otherwise, the arguments are interpreted as in a call to the
generic function.
setGeneric:def is supplied, and
the current function will become the default method for the
generic.
If def is supplied, this defines the generic function, and
no default method will exist (often a good feature, if the
function should only be available for a meaningful subset of all
objects).
Arguments group and valueClass are retained for
consistency with S-Plus, but are currently not used.
isGeneric:fdef argument is supplied, take this as the
definition of the generic, and test whether it is really a
generic, with f as the name of the generic. (This argument
is not available in S-Plus.)
removeGeneric:where supplied, just remove the version on this element
of the search list; otherwise, removes the first version
encountered.
standardGeneric:standardGeneric as their entire body. They can, however,
do any other computations as well.
The usual setGeneric (directly or through calling
setMethod) creates a function with a call to
standardGeneric.
dumpMethod:findFunction:generic is FALSE, ignore generic functions.
dumpMethods:signature is supplied only the methods matching this
initial signature are dumped. (This feature is not found in
S-Plus: don't use it if you want compatibility.)
signature:signature is to provide a check on
which arguments you meant, as well as clearer documentation in
your method specification. In addition, signature checks
that each of the elements is a single character string.
removeMethods:TRUE if f was a generic function,
FALSE (silently) otherwise.
If there is a default method, the function will be re-assigned as
a simple function with this definition.
Otherwise, the generic function remains but with no methods (so
any call to it will generate an error). In either case, a
following call to setMethod will consistently
re-establish the same generic function as before.
The R package methods implements, with a few exceptions, the programming interface for classes and methods in the book Programming with Data (John M. Chambers, Springer, 1998), in particular sections 1.6, 2.7, 2.8, and chapters 7 and 8.
While the programming interface for the methods package follows the reference, the R software is an original implementation, so details in the reference that reflect the S4 implementation may appear differently in R. Also, there are extensions to the programming interface developed more recently than the reference. For a discussion of details and ongoing development, see the web page http://developer.r-project.org/methodsPackage.html and the pointers from that page.
getMethod (also for selectMethod),
setGeneric,
setClass,
showMethods
## get the function "myFun" -- throw an error if 0 or > 1 versions visible:
findFuncStrict <- function(fName) {
allF <- findFunction(fName)
if(length(allF) == 0)
stop("No versions of ",fName," visible")
else if(length(allF) > 1)
stop(fName," is ambiguous: ", length(allF), " versions")
else
get(fName, allF[[1]])
}
try(findFuncStrict("myFun"))# Error: no version
lm <- function(x) x+1
try(findFuncStrict("lm"))# Error: 2 versions
findFuncStrict("findFuncStrict")# just 1 version
rm(lm)