is {methods}R Documentation

Is an Object from a Class

Description

is: With two arguments, tests whether object can be treated as from class2.

With one argument, returns all the super-classes of this object's class.

extends: Does the first class extend the second class? Returns maybe if the extension includes a test.

setIs: Defines class1 to be an extension of class2.

Usage

is(object, class2)

extends(class1, class2, maybe=TRUE)

setIs(class1, class2, test=NULL, coerce=NULL, replace=NULL, where=-1)

Arguments

object Any R object.
class1, class2 The names of the classes between which is relations are to be defined.
maybe What value to return if the relationship is conditional.
test, coerce, replace Functions optionally supplied to test whether the relation is defined, to coerce the object to class2, and to alter the object so that is(object, class2) is identical to value.
where Where to store the metadata defining the relationship. Default is the global environment.

Details

setIs:

The relationship can be conditional, if a function is supplied as the test argument. If a function is supplied as the coerce argument, this function will be applied to any class1 object in order to turn it into a class2 object.

Extension may imply that a class1 object contains a class2 object. The default sense of containing is that all the slots of the simpler class are found in the more elaborate one. If the replace argument is supplied as an S replacement function, this function will be used to implement as(obj, class2) <- value.

Author(s)

John Chambers

References

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.

Examples


## a class definition (see setClass for the example)
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 = structure(list(), x=numeric(), y=matrix(0,0,0), smooth= matrix(0,0,0)))
## Define a multi-curve to extend a single curve ONLY
## if the y data is one variable.
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")), curve = as.numeric(slot(obj, "curve")))})


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