| validObject {methods} | R Documentation |
The validity of object related to its class definition is
tested. If the object is valid, TRUE is returned; otherwise,
either a vector of strings describing validity failures is returned,
or an error is generated (according to whether test is
TRUE). Optionally, all slots in the object can also be validated.
The function setValidity sets the validity method of a class
(but more normally, this method will be supplied as the
validity argument to setClass). The method
should be a function of one object that returns TRUE or a
description of the non-validity.
validObject(object, test = FALSE, complete = FALSE) setValidity(Class, method, where = topenv(parent.frame()) )
object |
Any object, but not much will happen unless the object's class has a formal definition. |
test |
logical; if TRUE and validity fails, the
function returns a vector of strings describing the problems. If
test is FALSE (the default) validity failure generates
an error. |
complete |
logical; if TRUE, validity methods will be
applied recursively to any of the slots that have such methods. |
Class |
the name or class definition of the class whose validity method is to be set. |
method |
a validity method; that is, either NULL or a
function of one argument (the object). Like
validObject, the function should return TRUE if the
object is valid, and one or more descriptive strings if any problems
are found. Unlike validObject, it should never generate an
error.
|
where |
the modified class definition will be stored in this environment. |
Note that validity methods do not have to check validity of
superclasses: the logic of validObject ensures these tests are
done once only. As a consequence, if one validity method wants to use
another, it should extract and call the method from the other
definition of the other class by calling getValidity: it
should not call validObject.
Validity testing takes place “bottom up”: Optionally, if
complete=TRUE, the validity of the object's slots, if any, is
tested. Then, in all cases, for each of the classes that this class
extends (the “superclasses”), the explicit validity method of
that class is called, if one exists. Finally, the validity method of
object's class is called, if there is one.
Testing generally stops at the first stage of finding an error, except that all the slots will be examined even if a slot has failed its validity test.
The standard validity test (with complete=FALSE) is applied
when an object is created via new with any optional
arguments (without the extra arguments the result is just the class
prototype object).
validObject returns TRUE if the object is valid.
Otherwise a vector of strings describing problems found, except that
if test is FALSE, validity failure generates an error,
with the corresponding strings in the error message.
The R package methods implements, with a few exceptions, the programming interface for classes and methods in the book Programming with Data (John M. Chambers, Springer, 1998), in particular sections 1.6, 2.7, 2.8, and chapters 7 and 8.
While the programming interface for the methods package follows
the reference, the R software is an original implementation, so
details in the reference that reflect the S4 implementation may appear
differently in R. Also, there are extensions to the programming
interface developed more recently than the reference. For a
discussion of details see ?Methods
and the links from that documentation.
setClass("track",
representation(x="numeric", y = "numeric"))
t1 <- new("track", x=1:10, y=sort(rnorm(10)))
## A valid "track" object has the same number of x, y values
validTrackObject <- function(x){
if(length(x@x) == length(x@y)) TRUE
else paste("Unequal x,y lengths: ", length(x@x), ", ", length(x@y),
sep="")
}
## assign the function as the validity method for the class
setValidity("track", validTrackObject)
## t1 should be a valid "track" object
validObject(t1)
## Now we do something bad
t2 <- t1
t2@x <- 1:20
## This should generate an error
## Not run: try(validObject(t2))
setClass("trackCurve",
representation("track", smooth = "numeric"))
## all superclass validity methods are used when validObject
## is called from initialize() with arguments, so this fails
## Not run: trynew("trackCurve", t2)
setClass("twoTrack", representation(tr1 = "track", tr2 ="track"))
## validity tests are not applied recursively by default,
## so this object is created (invalidly)
tT <- new("twoTrack", tr2 = t2)
## A stricter test detects the problem
## Not run: try(validObject(tT, complete = TRUE))