\Header{setMethod}{Create and Save a Method}
\alias{removeMethod}{setMethod}
\keyword{programming}{setMethod}
\keyword{classes}{setMethod}
\keyword{classes}{setMethod}
\keyword{methods}{setMethod}
\begin{Description}\relax
Create and save a formal method for a given function and list of classes.\end{Description}
\begin{Usage}
\begin{verbatim}
setMethod(f, signature=character(), definition, where=1, valueClass)

removeMethod(f, signature, where)
\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\code{f}] The character-string name of the generic function. 
\item[\code{signature}] A match of formal argument names for \code{f} with
the character-string names of corresponding classes.  This
argument can also just be the vector of class names, in which case
the first name corresponds to the first formal argument, the
next to the second formal argument, etc.
\item[\code{definition}] A function definition, which will become the method
called when the arguments in a call to \code{f} match the
classes in \code{signature}, directly or through inheritance. 
\item[\code{where}] The database in which to store the definition of the
method; by default, the current global environment.

For \code{removeMethod}, the default is the location of the (first)
instance of the method for this signature.
\item[\code{valueClass}] If supplied, this argument asserts that the
method will return a value of this class.  (At present this
argument is stored but not explicitly used.) 
\end{ldescription}
\end{Arguments}
\begin{Details}\relax
R methods for a particular generic function are stored in an object
of class \code{\Link{MethodsList}}, which in turn is stored with the
definition of the generic function.  The effect of calling
\code{setMethod} is to store \code{definition}  in a \code{MethodsList}
object in a definition of the generic function on database
\code{where}.   If no such function exists (on that database) one
will be created, by copying the generic function from where it is
found in the current search list.  Finally, if \code{f} doesn't
exist as a generic function, but there is an ordinary function of
the same name and the same formal arguments, a new generic function
is created, and the previous non-generic version of \code{f} becomes
the default method.

Methods are stored in a hierarchical structure, by formal arguments
to \code{f}:  see \code{\Link{MethodsList}} for details.  The class
names in the signature can be any formal class, plus predefined basic
classes such as \code{"numeric"}, \code{"character"}, and
\code{"matrix"}.  Two additional special class names can appear:
\code{"ANY"}, meaning that this argument can have any class at all;
and \code{"missing"}, meaning that this argument \emph{must not}
appear in the call in order to match this signature.  Don't confuse
these two:  if an argument isn't mentioned in a signature, it
corresponds implicitly to class \code{"ANY"}, not to
\code{"missing"}.  See the example below.

While \code{f} can correspond to methods defined on several packages
or databases, the underlying model is that these together make up
the definition for a single generic function.  When R proceeds to
select and evaluate methods for \code{f}, the methods on the current
search list are merged to form a single generic.  In particular, all
the versions of \code{f} and all the methods must correspond to the
same formal arguments (including, in the present definition, the
same default expressions for the arguments).  For compatibility with
S-Plus, the current implementation enforces this partly with a
warning and a reconstruction of a method that fails to match, but
don't count on this for the future:  Make the formal arguments of
\code{definition} match those of the generic..\end{Details}
\begin{Value}
These functions exist for their side-effect, in setting or removing a
method in the object defining methods for the specified generic.

The value returned by \code{removeMethod} is \code{TRUE} if a method
was found to be removed.\end{Value}
\begin{Author}\relax
John Chambers\end{Author}
\begin{References}\relax
The web page \url{http://www.omegahat.org/RSMethods/index.html} is the primary documentation.

The functions in this package emulate the facility for classes and methods described in
\emph{Programming with Data}, (John M. Chambers, Springer, 1998).  See this book
for further details and examples.\end{References}
\begin{SeeAlso}\relax
\link{Methods}, \code{\Link{MethodsList}} for details of the
implementation\end{SeeAlso}
\begin{Examples}
\begin{ExampleCode}


## methods for plotting track objects (see the example for setClass)
##
## First, with only one object as argument:
setMethod("plot", signature(x="track", y="missing"),
  function(x,  y, ...) plot(slot(x, "x"), slot(x, "y"), ...)
)
## Second, plot the data from the track on the y-axis against anything
## as the x data.
setMethod("plot", signature(y = "track"),
 function(x, y, ...) plot(x, slot(y, "y"), ...)
)
## and similarly with the track on the x-axis (using the short form of
## specification for signatures)
setMethod("plot", "track",
 function(x, y, ...) plot(slot(x, "y"), y,  ...)
)
t1 <- new("track", x=1:20, y=(1:20)^2)
tc1 <- new("trackCurve", t1)
slot(tc1, "smooth") <- smooth.spline(slot(tc1, "x"), slot(tc1, "y"))$y #$
plot(t1)
plot(qnorm(ppoints(20)), t1)
## An example of inherited methods.
setMethod("plot", c("trackCurve", "missing"),
function(x, y, ...) {
  plot(as(x, "track"))
  if(length(slot(x, "smooth") > 0))
    lines(slot(x, "x"), slot(x, "smooth"))
  }
)
## the plot of tc1 alone has an added curve; other uses of tc1
## are treated as if it were a "track" object.
plot(tc1)
plot(qnorm(ppoints(20)), tc1)

## defining methods for a special function.
## Although "[" and "length" are not ordinary functions
## methods can be defined for them.
setMethod("[", "track",
  function(x, i, j, ..., drop) {
    x@x <- x@x[i]; x@y <- x@y[i]
    x
  })
plot(t1[1:15])

setMethod("length", "track", function(x)length(x@y))
length(t1)

## methods can be defined for missing arguments as well
setGeneric("summary") ## make the function into a generic

## A method for summary()
## The method definition can include the arguments, but
## if they're omitted, class "missing" is assumed.

setMethod("summary", "missing", function() "<No Object>")


\end{ExampleCode}
\end{Examples}

