UseMethod(name) NextMethod(name, object, ...) methods(generic.function, class)
An R ``object'' is a data object which has a class
attribute.
A class attribute is a vector of character strings giving the names of
the classes which the object ``inherits'' from. When a generic
function fun
is applied to an object with class attribute
c("first", "second")
, the system searches for a function called
fun.first
and, if it finds it, applied it to the object. If no
such function is found a function called fun.second
is tried.
If no class name produces a suitable function, the function
fun.default
is used.
methods
can be used to find out about the methods for a
particular generic function or class. See the examples below for
details.
Now for some obscure details that need to appear somewhere. These
comments will be slightly different than those in Appendix A of the
White S Book. UseMethod
creates a ``new'' function call with
arguments matched as they came in to the generic. Any local variables
defined before the call to UseMethod
are retained (!?). Any
statements after the call to UseMethod
will not be evaluated as
UseMethod
does not return.
NextMethod
invokes the next method (determined by the
class). It does this by creating a special call frame for that
method. The arguments will be the same in number, order and name as
those to the current method but their values will be promises to
evaluate their name in the current method and environment. Any
arguments matched to ...
are handled specially. They are
passed on as the promise that was supplied as an argument to the
current environment. (S does this differently!) If they have been
evaluated in the current (or a previous environment) they remain
evaluated.
methods
function was written by Martin Maechler.class
methods(summary) methods(print) methods(class = data.frame) methods("[")#- does not list the C-internal ones...