R: Test the Validity of an Object

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))

[Package methods version 3.1.2 Index]