[Rd] validObject does not check validity of slots

[Martin Morgan]

Thanks John for the reply and explanation. I sometimes use validObject
interactively, and in those circumstances it might be nice to be able
to require recursive validity checking, e.g., with an optional
argument.

Martin

John Chambers <jmc at r-project.org> writes:

> The problem is over-ambitious documentation.  Recursively running
> the checks on slots for all validObject calls would be a fairly
> serious efficiency hit.  Objects are checked for validity when
> created, other than as the default object, so assuming the slot
> objects to be as claimed is reasonable if they haven't been
> corrupted later on.  We'll update the documentation.
>
> Validity checking is a tricky business in general.  R validates new
> objects, but users can turn valid objects into invalid objects in
> cases where slots have to match in special ways (you can't apply
> validObject each time a slot changes, since the change may be part
> of a bigger computation that _will_ produce a valid object). 
> Similarly, constraints on the elements can't be checked each time an
> element or subset of the object changes, if the changes have to be
> done in stages.   Systems that "commit" top-level assignments can
> check then, but R does not have that distinction.
>
> Martin Morgan wrote:
>
>           The documentation for validObject suggests that slots are
> checked for validity, but validObject seems only to check that the
> slot has something claiming to be correct; validObject(obj) does not
> perform the equivalent of validObject(obj at y) for slot y.
>
> This is also the second problem issue reported in
>
> http://tolstoy.newcastle.edu.au/R/devel/05/03/0151.html
>
> Relevant documentation, an example, and sessionInfo follow.
>
> Martin
>
> validObject             package:methods             R Documentation
>
> Arguments:
>      ...
>      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.
>      ...
> Details:
>
>      Validity testing takes place "bottom up":  first the validity of
>      the object's slots, if any, is tested.  
>      ...
>
> setClass("foo",
>          representation( x="numeric" ),
>          validity = function( object ) object at x > 0 )
> setClass("bar",
>          representation( y="foo", z="numeric" ),
>          validity = function( object ) object at z > 0 )
> obj <- new( "bar", y = new( "foo", x=1 ), z = 1 )
>
> and then...
>
>   
>
>                     validObject( obj )
>     
>
>
>      [1] TRUE
> ## invalidate obj at y
>   
>
>                     obj at y@x <- -1
> validObject( obj at y )                  # right, this is not valid
>     
>
>
>      Error in validObject(obj at y) : invalid class "foo" object: FALSE
>   
>
>                     ## obj at y is invalid, but obj is valid?
> validObject( obj )                    # should be invalid?
>     
>
>
>      [1] TRUE
>
>
>
>   
>
>                     sessionInfo()
>     
>
>
>      Version 2.3.0 Under development (unstable) (2006-03-03 r37471) 
> x86_64-unknown-linux-gnu 
>
> attached base packages:
> [1] "methods"   "stats"     "graphics"  "grDevices" "utils"     "datasets" 
> [7] "base"
>
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