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 functions getValidity
and setValidity
get and set
the validity method of a class. This method is a function of one
object that returns TRUE
or a description of the non-validity.
validObject(object, test) getValidity(ClassDef) setValidity(ClassDef, method)
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. |
ClassDef |
The name 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.
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.
John Chambers
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.
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 try(validObject(t1))