setClass {methods} | R Documentation |
Create a formally defined class with specified slots and/or relationships to other classes. Also functions to remove a class definition, to test whether a class has been defined, to test whether an object is a class definition, and to reset the internal definition of a class.
setClass(Class, representation, prototype, contains=character(), validity, access, where=1, version=FALSE) removeClass(Class, where=-1) isClass(Class, formal=TRUE) isClassDef(object) getClasses(where) resetClass(Class)
Class |
character string name for the class |
representation |
the slots that the new class should have
and/or other classes that this class extends. Usually a call to
the representation function. |
prototype |
an object (usually a list) providing the default data for the slots specified in the representation. |
contains |
what classes does this class extend? (These are called superclasses in some languages.) When these classes have slots, all their slots will be contained in the new class as well. |
where |
What environment to use to store or remove the definition (as metadata).
By default, uses the global environment for setClass and
searches for a definition to remove, for removeClass . |
validity, access, version |
Control arguments included for compatibility with the S-Plus API, but not currently used. |
x |
an arbitrary object. |
formal |
Should a formal definition be required? |
object |
any R object. |
These are the functions that create and manipulate formal class definitions. Brief documentation is provided below. See the references for an introduction and for more details.
setClass
:"classRepEnvironment"
, and store this
(hidden) in the specified environment or database. Objects can be
created from the class (e.g., by calling new
),
manipulated (e.g., by accessing the object's slots), and methods
may be defined including the class name in the signature (see
setMethod
).
removeClass
:where=0
, that's all it does. Otherwise, it removes the
version from the specified environment or database (from the global
environment by default).
isClass
:formal
is for
compatibility and is ignored.)
isClassDef
:getClass
, the complete
definition of a class with its extensions, or to getClassDef
, the local
definition of the class).
getClasses
:unclass
:
For classes that extend a single other class (e.g., a basic class
such as "numeric"
) the result is an object of that class.
resetClass
:This function is called when aspects of the class definition are changed. You would need to call it explicitly if you changed the definition of a class that this class extends (but doing that in the middle of a session is living dangerously, since it may invalidate existing objects).
Defining new classes that inherit from (``extend'') other classes is a powerful technique, but has to be used carefully and not over-used. Otherwise, you will often get unintended results when you start to compute with objects from the new class.
As shown in the examples below, the simplest and safest form of inheritance is to start with an explicit class, with some slots, that does not extend anything else. It only does what we say it does.
Then extensions will add some new slots and new behavior.
Another variety of extension starts with one of the basic classes, perhaps with the intension of modifying R's standard behavior for that class. Perfectly legal and sometimes quite helpful, but you may need to be more careful in this case: your new class will inherit much of the behavior of the basic (informally defined) class, and the results can be surprising. Just proceed with caution and plenty of testing.
As an example, the class "matrix"
is included in the
pre-defined classes, to behave essentially as matrices do without
formal class definitions. Suppose we don't like all of this; in
particular, we want the default matrix to have 0 rows and columns (not
1 by 1 as it is now).
setClass("myMatrix", "matrix", prototype = matrix(0,0,0))
The arguments above illustrate two short-cuts relevant to such
examples. We abbreviated the representation
argument to the
single superclass, because the new class doesn't add anything to the
representation of class "matrix"
. Also, we provided an object
from the superclass as the prototype, not a list of slots.
John Chambers
The web page 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 Programming with Data, (John M. Chambers, Springer, 1998). See this book for further details and examples.
## A simple class with two slots setClass("track", representation(x="numeric", y="numeric")) ## A class extending the previous, adding one more slot setClass("trackCurve", representation("track", smooth = "numeric")) ## A class similar to "trackCurve", but with different structure ## allowing matrices for the "y" and "smooth" slots setClass("trackMultiCurve", representation(x="numeric", y="matrix", smooth="matrix"), prototype = list(x=numeric(), y=matrix(0,0,0), smooth= matrix(0,0,0))) ## ## Suppose we want trackMultiCurve to be like trackCurve when there's only ## one column ## First, the wrong way. try(setIs("trackMultiCurve", "trackCurve", test = function(obj) {ncol(slot(obj, "y")) == 1})) ## why didn't that work? You can only override the slots "x", "y", and "smooth" ## if you provide an explicit coerce function to correct any inconsistencies: setIs("trackMultiCurve", "trackCurve", test = function(obj) {ncol(slot(obj, "y")) == 1}, coerce = function(obj) { new("trackCurve", x = slot(obj, "x"), y = as.numeric(slot(obj,"y")), smooth = as.numeric(slot(obj, "smooth")))})