\Header{show}{Show an Object}
\keyword{programming}{show}
\begin{Description}\relax
Display the object, by printing, plotting or whatever suits its class.

The function \code{show} exists to be specialized by methods; the
default method calls \code{showDefault}.

With library \code{methods} attached, methods for \code{show} will
usually be invoked for automatic printing (see the details).

The function \code{showDefault} allows redirection of output and
optional use of old-style print methods, but normally will not be
called directly.\end{Description}
\begin{Usage}
\begin{verbatim}
show(object)

showDefault(object, printTo = stdout(), oldMethods = TRUE)
\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\code{object}] Any R object
\item[\code{printTo}] Either a file or \link{connection}, or else
\code{FALSE}.  In the latter case, the lines of text that would
have been printed are returned as the value of the call (in a
character vector with one element per line of output).

\item[\code{oldMethods}] Should old-style print methods be used for this
object?  \code{TRUE} by default if called directly, but \code{FALSE}
when called from the methods package for automatic printing (to
avoid potential recursion; see the
details below).

\end{ldescription}
\end{Arguments}
\begin{Details}\relax
The \code{methods} package overrides the base definition of
\code{print.default} to arrange for automatic printing to honor
methods for the function \code{show}.  This does not quite manage to
override old-style printing methods, since the automatic printing in
the evaluator will look first for the old-style method.

If you have a class \code{myClass} and want to define a method for
\code{show}, all will be well unless there is already a function named
\code{print.myClass}.  In that case, to get your method dispatched for
automatic printing, it will have to be a method for \code{print}.  A
slight cheat is to override the function \code{print.myClass} yourself,
and then call that function also in the method for \code{show}
with signature \code{"myClass"}.\end{Details}
\begin{Value}
\code{show} returns an invisible \code{NULL}.

For \code{showDefault}, if \code{printTo} is \code{FALSE}, the value
is a character vector containing the lines that would otherwise have
been printed.\end{Value}
\begin{SeeAlso}\relax
\code{\Link{showMethods}} prints all the methods for one or more
functions;
\code{\Link{showMlist}} prints individual methods lists; 
\code{\Link{showClass}} prints class definitions.
Neither of the latter two normally needs to be called directly.\end{SeeAlso}
\begin{Examples}
\begin{ExampleCode}
## following the example shown in the setMethod documentation ...
setClass("track",
         representation(x="numeric", y="numeric"))
setClass("trackCurve", 
         representation("track", smooth = "numeric"))

t1 <- new("track", x=1:20, y=(1:20)^2)

tc1 <- new("trackCurve", t1)

setMethod("show", "track",
  function(object)print(rbind(x = object@x, y=object@y))
)
## The method will now be used for automatic printing of t1

t1

  [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10] [,11] [,12]
x    1    2    3    4    5    6    7    8    9    10    11    12
y    1    4    9   16   25   36   49   64   81   100   121   144
  [,13] [,14] [,15] [,16] [,17] [,18] [,19] [,20]
x    13    14    15    16    17    18    19    20
y   169   196   225   256   289   324   361   400

## and also for tc1, an object of a class that extends "track"
tc1

  [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10] [,11] [,12]
x    1    2    3    4    5    6    7    8    9    10    11    12
y    1    4    9   16   25   36   49   64   81   100   121   144
  [,13] [,14] [,15] [,16] [,17] [,18] [,19] [,20]
x    13    14    15    16    17    18    19    20
y   169   196   225   256   289   324   361   400

\end{ExampleCode}
\end{Examples}

