\HeaderA{representation}{Construct a  Representation or a Prototype for a Class Definition}{representation}
\aliasA{prototype}{representation}{prototype}
\keyword{programming}{representation}
\keyword{classes}{representation}
\begin{Description}\relax
In calls to
\code{\LinkA{setClass}{setClass}}, these two functions construct,
respectively, the \code{representation} and \code{prototype}
arguments.  They do various checks and handle special cases.  You're
encouraged to use them when defining classes that, for
example, extend other classes as a data part or have multiple
superclasses, or that combine extending a class and slots.
\end{Description}
\begin{Usage}
\begin{verbatim}
representation(...)
prototype(...)
\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\code{...}] The call to representation takes arguments that are single character
strings.  Unnamed arguments are classes that a newly defined class
extends; named arguments name the explicit slots in the new class,
and specify what class each slot should have.

In the call to \code{prototype}, if an unnamed argument is
supplied, it unconditionally forms the basis for the prototype
object.  Remaining arguments are taken to correspond to slots of
this object.  It is an error to supply more than one unnamed argument.

\end{ldescription}
\end{Arguments}
\begin{Details}\relax
The \code{representation} function applies tests for the validity of
the arguments.  Each must specify the name of a class.

The classes named don't have to exist when \code{representation} is
called, but if they do, then the function will check for any duplicate
slot names introduced by each of the inherited classes.

The arguments to \code{prototype} are usually named initial values
for slots, plus an optional first argument that gives the object
itself.  The unnamed argument is typically useful if there is a data
part to the definition (see the examples below).
\end{Details}
\begin{Value}
The value pf \code{representation}  is just the list of arguments, after these have been checked
for validity.

The value of \code{prototype} is the object to be used as the
prototype.  Slots will have been set consistently with the
arguments, but the construction does \emph{not} use the class
definition to test validity of the contents (it hardly can, since
the prototype object is usually supplied to create the definition).
\end{Value}
\begin{References}\relax
The R package \pkg{methods} implements, with a few exceptions, the
programming interface for classes and methods in the book
\emph{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 \pkg{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 
\url{http://developer.r-project.org/methodsPackage.html} and the
pointers from that page.
\end{References}
\begin{SeeAlso}\relax
\code{\LinkA{setClass}{setClass}}
\end{SeeAlso}
\begin{Examples}
\begin{ExampleCode}
## representation for a new class with a directly define slot "smooth"
## which should be a "numeric" object, and extending class "track"
representation("track", smooth ="numeric")


setClass("Character",representation("character"))
setClass("TypedCharacter",representation("Character",type="character"),
          prototype(character(0),type="plain"))
ttt <- new("TypedCharacter", "foo", type = "character")


setClass("num1", representation(comment = "character"),
         contains = "numeric",
         prototype = prototype(pi, comment = "Start with pi"))



\end{ExampleCode}
\end{Examples}

