methods (version 3.3)

GenericFunctions: Tools for Managing Generic Functions

Description

The functions documented here manage collections of methods associated with a generic function, as well as providing information about the generic functions themselves.

Usage

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 = missing(where))
setReplaceMethod(f, ..., where = topenv(parent.frame()))
getGenerics(where, searchForm = FALSE)

Arguments

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. Signatures are matched to the arguments specified in the signature slot of the generic function (see the Details section of the setMethod documentation).

The signature argument to dumpMethods is ignored (it was used internally in previous implementations).

file

The file or connection 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").

References

Chambers, John M. (2008) Software for Data Analysis: Programming with R Springer. (For the R version.)

Chambers, John M. (1998) Programming with Data Springer (For the original S4 version.)

See Also

getMethod (also for selectMethod), setGeneric, setClass, showMethods

Examples

require(stats) # for lm

## 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)

## because nosegfault runs standardGeneric w/o the methods package, nothing
## really gets tested.  The following check that it catches some errors
mustDie <- function(expr)
   stopifnot(is(tryCatch(expr, error=function(e)e), "error"))

mustDie(standardGeneric()) # 3 tests of requiring a single string
mustDie(standardGeneric(NULL))
mustDie(standardGeneric(""))
mustDie(standardGeneric("notAGenericFunction"))
mustDie(standardGeneric("show"))  # a generic, but not called from its body

## method dumping ------------------------------------

setClass("A", representation(a="numeric"))
setMethod("plot", "A", function(x,y,...){ cat("A meth
") })
dumpMethod("plot","A", file="")
setMethod("plot", "A",
function (x, y, ...)
{
    cat("AAAAA\n")
}
)tmp <- tempfile()
dumpMethod("plot","A", file=tmp)
## now remove, and see if we can parse the dump
stopifnot(removeMethod("plot", "A"))
source(tmp)
stopifnot(is(getMethod("plot", "A"), "MethodDefinition"))

## same with dumpMethods() :
setClass("B", contains="A")
setMethod("plot", "B", function(x,y,...){ cat("B ...
") })
dumpMethods("plot", file=tmp)
stopifnot(removeMethod("plot", "A"),
          removeMethod("plot", "B"))
source(tmp)
stopifnot(is(getMethod("plot", "A"), "MethodDefinition"),
          is(getMethod("plot", "B"), "MethodDefinition"))

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