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

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% Copyright 1995-2007 R Core Team

% Distributed under GPL 2 or later

\name{classRepresentation-class}

\docType{class}

\alias{classRepresentation-class}

\title{Class Objects }

\description{  These are the objects that hold the definition of

  classes of objects.  They are constructed and stored as meta-data by

  calls to the function \code{\link{setClass}}.  Don't manipulate them

  directly, except perhaps to look at individual slots. }

\section{Slots}{

  \describe{

    \item{\code{slots}:}{A named list of the slots in this class; the

      elements of the list are the classes to which the slots must

      belong (or extend), and the names of the list gives the

      corresponding slot names.}

    \item{\code{contains}:}{A named list of the classes this class

      \sQuote{contains}; the elements of the list are objects of

      \code{\linkS4class{SClassExtension}}. The list may be only the

      direct extensions or all the currently known extensions (see the

      details).}

    \item{\code{virtual}:}{Logical flag, set to \code{TRUE} if this is

      a virtual class.}

    \item{\code{prototype}:}{The object that represents the standard

      prototype for this class; i.e., the data and slots returned by a

      call to \code{\link{new}} for this class with no special

      arguments.  Don't mess with the prototype object directly.}

    \item{\code{validity}:}{Optionally, a function to be used to test

      the validity of objects from this class.

      See \code{\link{validObject}}.}

    \item{\code{access}:}{Access control information.  Not currently used.}

    \item{\code{className}:}{The character string name of the class.}

    \item{\code{package}:}{The character string name of the package to

      which the class belongs.  Nearly always the package on which the

      metadata for the class is stored, but in operations such as

      constructing inheritance information, the internal package name

      rules.}

    \item{\code{subclasses}:}{A named list of the classes known to

      extend this class'; the elements of the list are objects of class

      \code{\linkS4class{SClassExtension}}.  The list is currently only

      filled in when completing the class definition (see the details).}

    \item{\code{versionKey}:}{Object of class \code{"externalptr"};

      eventually will perhaps hold some versioning information, but not

      currently used. }

    \item{\code{sealed}:}{Object of class \code{"logical"}; is this

      class sealed?  If so, no modifications are allowed. }

  }

}

\details{

  Class definitions are stored as metadata in various packages.

  Additional metadata supplies information on inheritance (the result of

  calls to \code{\link{setIs}}).  Inheritance information implied by the

  class definition itself (because the class contains one or more other

  classes) is also constructed automatically.

  When a class is to be used in an R session, this information is

  assembled to complete the class definition.  The completion is a

  second object of class \code{"classRepresentation"}, cached for the

  session or until something happens to change the information.  A call

  to \code{\link{getClass}} returns the completed definition of a class;

  a call to \code{\link{getClassDef}} returns the stored definition

  (uncompleted).

  In particular, completion fills in the upward- and downward-pointing

  inheritance information for the class, in slots \code{contains} and

  \code{subclasses} respectively.  It's in principle important to note

  that this information can depend on which packages are installed,

  since these may define additional subclasses or superclasses.

}

\seealso{

  See function \code{\link{setClass}} to supply the information in the

  class definition.

  See \link{Classes} for a more basic discussion of class information.

}

\keyword{classes}