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% File src/library/methods/man/setGeneric.Rd
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% Part of the R package, https://www.R-project.org
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% Copyright 1995-2016 R Core Team
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% Distributed under GPL 2 or later
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\name{setGroupGeneric}
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\alias{setGroupGeneric}
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\title{Create a Group Generic Version of a Function}
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\description{
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The \code{setGroupGeneric} function behaves like \code{\link{setGeneric}}
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except that it constructs a group generic function, differing in two
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ways from an ordinary generic function. First, this function cannot
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be called directly, and the body of the function created will contain
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a stop call with this information. Second, the group generic function
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contains information about the known members of the group, used to
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keep the members up to date when the group definition changes, through
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changes in the search list or direct specification of methods, etc.
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All members of the group must have the identical argument list.
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}
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\usage{
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setGroupGeneric(name, def= , group=list(), valueClass=character(),
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knownMembers=list(), package= , where= )
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}
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\arguments{
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\item{name}{the character string name of the generic function.
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}
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\item{def}{A function object. There isn't likely to be an existing
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nongeneric of this name, so some function needs to be supplied. Any
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known member or other function with the same argument list will do,
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because the group generic cannot be called directly.
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}
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\item{group, valueClass}{arguments to pass to
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\code{\link{setGeneric}}.
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}
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\item{knownMembers}{the names of functions that are
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known to be members of this group. This information is used to
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reset cached definitions of the member generics when information
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about the group generic is changed.
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}
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\item{package, where}{passed to \code{\link{setGeneric}}, but
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obsolete and to be avoided.}
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}
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\value{
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The \code{setGroupGeneric} function exists for its side effect: saving the
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generic function to allow methods to be specified later. It returns
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\code{name}.
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}
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\references{
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\bibshow{R:Chambers:2016}
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}
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\examples{
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\dontrun{
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## the definition of the "Logic" group generic in the methods package
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setGroupGeneric("Logic", function(e1, e2) NULL,
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knownMembers = c("&", "|"))
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}
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}
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\seealso{
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\code{\link{Methods_Details}} and the links there for a general discussion,
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\code{\link{dotsMethods}} for methods that dispatch on
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\code{\dots}, and \code{\link{setMethod}} for method definitions.
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}
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\keyword{ programming }
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\keyword{ methods }
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