\Header{MethodsList}{MethodsList Objects}
\alias{emptyMethodsList}{MethodsList}
\alias{finalDefaultMethod}{MethodsList}
\alias{inheritedSubMethodLists}{MethodsList}
\alias{insertMethod}{MethodsList}
\alias{insertMethodInEmptyList}{MethodsList}
\alias{linearizeMlist}{MethodsList}
\alias{listFromMlist}{MethodsList}
\alias{loadMethod}{MethodsList}
\alias{loadMethod,ANY-method}{MethodsList}
\alias{loadMethod,MethodDefinition-method}{MethodsList}
\alias{loadMethod,MethodWithNext-method}{MethodsList}
\alias{loadMethod-methods}{MethodsList}
\alias{makeMethodsList}{MethodsList}
\alias{mergeMethods}{MethodsList}
\alias{print.MethodsList}{MethodsList}
\alias{showMlist}{MethodsList}
\alias{SignatureMethod}{MethodsList}
\keyword{internal}{MethodsList}
\begin{Description}\relax
These functions create and manipulate \code{MethodsList} objects, the
objects used in R to store methods for dispatch.  You should not call
any of these functions from code that you want to port to S-Plus.
Instead, use the functions described in the references.
\end{Description}
\begin{Usage}
\begin{verbatim}
MethodsList(.ArgName, ...)

makeMethodsList(object, level=1)

SignatureMethod(names, signature, definition)

insertMethod(mlist, signature, args, def, cacheOnly)

inheritedSubMethodLists(object, thisClass, mlist, ev)

showMlist(mlist, includeDefs = TRUE, inherited = TRUE,
   classes, useArgNames, printTo = stdout() )

## S3 method for class 'MethodsList':
print(x, ...)

listFromMlist(mlist, prefix = list())

linearizeMlist(mlist, inherited = TRUE)

finalDefaultMethod(mlist, fname = "NULL")

mergeMethods(m1, m2, genericLabel)

loadMethod(method, fname, envir)

\end{verbatim}
\end{Usage}
\begin{Details}\relax
Note that \code{MethodsList} objects represent methods only in the \R{}
implementation.  You can use them to find or manipulate information about
methods, but avoid doing so if you want your code to port to S-Plus.
\end{Details}
\begin{Section}{Details}
\describe{

\item[\code{MethodsList}:] Create a MethodsList object out of the arguments.

Conceptually, this object is a named collection of methods to be
dispatched when the (first) argument in a function call matches
the class corresponding to one of the names.  A final, unnamed
element (i.e., with name \code{""}) corresponds to the default
method.

The elements can be either a function, or another MethodsList.  In
the second case, this list implies dispatching on the second
argument to the function using that list, given a selection of
this element on the first argument.  Thus, method dispatching on
an arbitrary number of arguments is defined.

MethodsList objects are used primarily to dispatch OOP-style
methods and, in R, to emulate S4-style methods.


\item[\code{SignatureMethod}:] construct a MethodsList object containing (only) this method,
corresponding to the signature; i.e., such that
\code{signature[[1]]} is the match for the first argument,
\code{signature[[2]]} for the second argument, and so on.  The
string \code{"missing"} means a match for a missing argument, and
\code{"ANY"} means use this as the default setting at this level.

The first argument is the argument names to be used for dispatch
corresponding to the signatures.


\item[\code{insertMethod}:] insert the definition \code{def} into the MethodsList object,
\code{mlist}, corresponding to the signature.  By default, insert
it in the slot \code{"methods"}, but \code{cacheOnly=TRUE} inserts
it into the \code{"allMethods"} slot (used for dispatch but not saved).


\item[\code{inheritedSubMethodLists}:] Utility function to match the object  or the class (if the object
is \code{NULL}) to the elements of a methods list.
Used in finding inherited methods, and not meant to be called
directly.


\item[\code{showMlist}:] Prints the contents of the MethodsList.  If \code{includeDefs} the
signatures and the corresonding definitions will be printed;
otherwise, only the signatures.

The function calls itself recursively: \code{prev} is the
previously selected classes.


\item[\code{listFromMlistForPrint}:] Undo the recursive nature of the methods list, making a list of
function defintions, with the names of the list being the
corresponding signatures (designed for printing; for looping over
the methods, use \code{\Link{listFromMlist}} instead).

The function calls itself recursively: \code{prev} is the
previously selected classes.


\item[\code{finalDefaultMethod}:] The true default method for the methods list object \code{mlist}
(the method that matches class \code{"ANY"} for as many arguments
as are used in methods matching for this generic function).  If
\code{mlist} is null, returns the function called \code{fname}, or
\code{NULL} if there is no such function.


\item[\code{mergeMethods}:] Merges the methods in the second MethodsList object into the
first, and returns the merged result.  Called from
\code{\Link{getAllMethods}}.  For a primitive function,
\code{genericLabel} is supplied as the name of the generic.


\item[\code{loadMethod}:] Called, if necessary, just before a call to \code{method} is
dispatched in the frame \code{envir}.  The function exists so that
methods can be defined for special classes of objects.  Usually
the point is to assign or modify information in the frame
environment to be used evaluation.  For example, the standard
class \code{MethodDefinition} has a method that stores the target
and defined signatures in the environment.  Class
\code{MethodWithNext} has a method taking account of the
mechanism for storing the method to be used in a call to
\code{\Link{callNextMethod}}.

Any methods defined for \code{loadMethod} must return the function
definition to be used for this call; typically, this is just the
\code{method} argument.

}
\end{Section}
\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}

