validObject {methods}

R Documentation

Test the Validity of an Object

Description

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.

Usage

validObject(object, test = FALSE, complete = FALSE)

setValidity(Class, method, where = topenv(parent.frame()) )

getValidity(ClassDef)

Arguments

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.
ClassDef	a class definition object, as from getClassDef.
method	a validity method; that is, either NULL or a function of one argument (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.

Details

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).

An attempt is made to fix up the definition of a validity method if its argument is not object.

Value

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.

References

Chambers, John M. (2008) Software for Data Analysis: Programming with R Springer. (For the R version.)

Chambers, John M. (1998) Programming with Data Springer (For the original S4 version.)

See Also

setClass; class classRepresentation.

Examples

setClass("track",
          representation(x="numeric", y = "numeric"))
t1 <- new("track", x=1:10, y=sort(stats::rnorm(10)))
## A valid "track" object has the same number of x, y values
validTrackObject <- function(object) {
    if(length(object@x) == length(object@y)) TRUE
    else paste("Unequal x,y lengths: ", length(object@x), ", ",
               length(object@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))

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