| 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).
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) 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 |
If test is 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. |
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 any
slots or 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”: first the validity
of the object's slots, if any, is tested. Then 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.
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 and ongoing development, see the web page http://developer.r-project.org/methodsPackage.html and the pointers from that page.
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
t1@x <- 1:20
## This should generate an error
## Not run: try(validObject(t1))