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% File src/library/methods/man/genericFunction-class.Rd

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\name{genericFunction-class}

\docType{class}

\alias{genericFunction-class}

\alias{groupGenericFunction-class}

\title{Generic Function Objects }

\description{

  Generic functions (objects from or extending class

  \code{genericFunction}) are extended function objects,

  containing information used in creating and dispatching methods for

  this function.  They also identify the package associated with the

  function and its methods.

}

\section{Objects from the Class}{

  Generic functions are created and assigned by

  \code{\link{setGeneric}} or \code{\link{setGroupGeneric}} and, indirectly, by

  \code{\link{setMethod}}.

  As you might expect \code{\link{setGeneric}} and

  \code{\link{setGroupGeneric}} create objects of class

  \code{"genericFunction"} and \code{"groupGenericFunction"} respectively.

}

\section{Slots}{

  \describe{

    \item{\code{.Data}:}{Object of class \code{"function"}, the

        function definition of the generic, usually created

        automatically as a call to \code{\link{standardGeneric}}. }

    \item{\code{generic}:}{Object of class \code{"character"}, the

        name of the generic function. }

    \item{\code{package}:}{Object of class \code{"character"}, the

        name of the package to which the function definition belongs

        (and \emph{not} necessarily where the generic function is

        stored). If the package is not specified explicitly in the

        call to \code{setGeneric}, it is usually the package on which

        the corresponding non-generic function exists. }

    \item{\code{group}:}{Object of class \code{"list"}, the group or

        groups to which this generic function belongs.  Empty by default. }

    \item{\code{valueClass}:}{Object of class \code{"character"}; if

        not an empty character vector, identifies one or more classes.  It is

        asserted that all methods for this function return objects

        from these class (or from classes that extend them). }

    \item{\code{signature}:}{Object of class \code{"character"}, the

        vector of formal argument names that can appear in the

        signature of methods for this generic function.  By default,

        it is all the formal arguments, except for \dots.  Order

        matters for efficiency:  the most commonly used arguments in

        specifying methods should come first. }

    \item{\code{default}:}{Object of class \code{"optionalMethod"}

        (a union of classes \code{"function"} and \code{"NULL"}), containing

        the default method for this function if any.  Generated

        automatically and used to initialize method dispatch. }

    \item{\code{skeleton}:}{Object of class \code{"call"}, a slot used

        internally in method dispatch.  Don't expect to use it

        directly.}

  }

}

\section{Extends}{

  Class \code{"function"}, from data part.\cr

  Class \code{"OptionalMethods"}, by class \code{"function"}.\cr

  Class \code{"PossibleMethod"}, by class \code{"function"}.

}

\section{Methods}{

  Generic function objects are used in the creation and dispatch of

  formal methods; information from the object is used to create methods

  list objects and to merge or update the existing methods for this

  generic.

}

\keyword{classes}