From mtmorgan at fhcrc.org  Tue Mar  7 17:50:03 2006
From: mtmorgan at fhcrc.org (Martin Morgan)
Date: Tue, 07 Mar 2006 08:50:03 -0800
Subject: [Rd] validObject does not check validity of slots
In-Reply-To: <440CDC8B.9080905@r-project.org> (John Chambers's message of
	"Mon, 06 Mar 2006 20:06:19 -0500")
References: <6phk6b7zf22.fsf@gopher3.fhcrc.org>
	<440CDC8B.9080905@r-project.org>
Message-ID: <6ph1wxeyzb8.fsf@gopher3.fhcrc.org>

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"
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>
>



[Rd] validObject does not check validity of slots
Martin Morgan