\HeaderA{MethodsList}{MethodsList Objects}{MethodsList}
\aliasA{emptyMethodsList}{MethodsList}{emptyMethodsList}
\aliasA{finalDefaultMethod}{MethodsList}{finalDefaultMethod}
\aliasA{inheritedSubMethodLists}{MethodsList}{inheritedSubMethodLists}
\aliasA{insertMethod}{MethodsList}{insertMethod}
\aliasA{insertMethodInEmptyList}{MethodsList}{insertMethodInEmptyList}
\aliasA{linearizeMlist}{MethodsList}{linearizeMlist}
\aliasA{listFromMlist}{MethodsList}{listFromMlist}
\aliasA{loadMethod}{MethodsList}{loadMethod}
\aliasA{loadMethod,ANY-method}{MethodsList}{loadMethod,ANY.Rdash.method}
\aliasA{loadMethod,MethodDefinition-method}{MethodsList}{loadMethod,MethodDefinition.Rdash.method}
\aliasA{loadMethod,MethodWithNext-method}{MethodsList}{loadMethod,MethodWithNext.Rdash.method}
\aliasA{loadMethod-methods}{MethodsList}{loadMethod.Rdash.methods}
\aliasA{makeMethodsList}{MethodsList}{makeMethodsList}
\aliasA{mergeMethods}{MethodsList}{mergeMethods}
\aliasA{MethodsListSelect}{MethodsList}{MethodsListSelect}
\aliasA{print.MethodsList}{MethodsList}{print.MethodsList}
\aliasA{showMlist}{MethodsList}{showMlist}
\aliasA{SignatureMethod}{MethodsList}{SignatureMethod}
\keyword{internal}{MethodsList}
\begin{Description}\relax
These functions create and manipulate \code{MethodsList} objects, the
objects formerly used in R to store methods for dispatch.  Use of
these objects is no longer required, and while not yet formally
deprecated, will rarely be a good idea.  Where methods dispatch is
to be studied, see \code{\LinkA{selectMethod}{selectMethod}}.  For computations
that iterate over methods or over method signatures, see
\code{\LinkA{findMethods}{findMethods}}, which returns a linearized methods list
to hold method definitions, usually more convenient for iteration
than the recursive \code{MethodsList} objects.
\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(), sigs. = TRUE, methods. = TRUE)

linearizeMlist(mlist, inherited = TRUE)

finalDefaultMethod(mlist, fname = "NULL")

mergeMethods(m1, m2, genericLabel)

loadMethod(method, fname, envir)

MethodsListSelect(f, env, mlist, fEnv, finalDefault, evalArgs,
                  useInherited, fdef, resetAllowed)

\end{verbatim}
\end{Usage}
\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 corresponding definitions will be printed;
otherwise, only the signatures.


\item[\code{listFromMlist}:] Undo the recursive nature of the methods list, making a list of
\code{list(sigs,methods)} of function definitions, i.e. of
matching signatures and methods.
\code{prefix} is the partial signature (a named list of classes)
to be prepended to the signatures in this object.  If \code{sigs.}
or \code{methods.} are \code{FALSE}, the resulting part of the
return value will be empty.

A utility function used to iterate over all the individual methods
in the object, it calls itself recursively.


\item[\code{linearizeMlist}:] Undo the recursive nature of the methods list, making a list of
function definitions, with the names of the list being the
corresponding signatures.

Designed for printing; for looping over the methods, use the above
\code{listFromMlist} instead.


\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 or no matching method is found, 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{\LinkA{getAllMethods}{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{\LinkA{callNextMethod}{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.


\item[\code{MethodsListSelect}] The function \code{MethodsListSelect} performs a full search
(including all inheritance and group generic information: see the
\LinkA{Methods}{Methods} documentation page for details on how this works).
The call returns a possibly revised methods list object,
incorporating any method found as part of the \code{allMethods}
slot.  This search was used by the evaluator when methods lists
were the metadata for methods dispatch.  This function is now deprecated.


}
\end{Section}
\begin{Note}\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{Note}
\begin{References}\relax
Chambers, John M. (2008)
\emph{Software for Data Analysis: Programming with R}
Springer.  (For the R version.)

Chambers, John M. (1998)
\emph{Programming with Data}
Springer (For the original S4 version.)
\end{References}

