MethodsList Objects

Description

These functions create and manipulate MethodsList objects, the objects formerly used in R to store methods for dispatch. Use of these objects is deprecated since R 3.2.0, as it will rarely be a good idea. Where methods dispatch is to be studied, see selectMethod. For computations that iterate over methods or over method signatures, see findMethods, which returns a linearized methods list to hold method definitions, usually more convenient for iteration than the recursive MethodsList objects.

Usage

listFromMlist(mlist, prefix = list(), sigs. = TRUE, methods. = TRUE)

linearizeMlist(mlist, inherited = TRUE)

finalDefaultMethod(method)

loadMethod(method, fname, envir)

##--------- These are all deprecated, since R 3.2.0 ----------

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, ...)

mergeMethods(m1, m2, genericLabel)

Details

listFromMlist:

Undo the recursive nature of the methods list, making a list of list(sigs,methods) of function definitions, i.e. of matching signatures and methods. prefix is the partial signature (a named list of classes) to be prepended to the signatures in this object. If sigs. or methods. are 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.

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 listFromMlist instead.

finalDefaultMethod:

The default method or NULL. With the demise of "MethodsList" objects, this function only checks that the value given it is a method definition, primitive or NULL.

loadMethod:

Called, if necessary, just before a call to method is dispatched in the frame 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 MethodDefinition has a method that stores the target and defined signatures in the environment. Class MethodWithNext has a method taking account of the mechanism for storing the method to be used in a call to callNextMethod.

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

References

Chambers, John M. (2008) Software for Data Analysis: Programming with R Springer. (For the R version.)

Chambers, John M. (1998) Programming with Data Springer (For the original S4 version.)