[Rd] How to debug reference classes?

John Chambers jmc at r-project.org
Fri Apr 8 03:12:17 CEST 2011


Good to know.  However, _please_ don't use the horrible kludge in the 
attr(..) expression.  From my experimenting, it worked fine just to say:

mtrace(edit, from = xx)

and even if that did not work, from = as.environment(xx) is identical in 
effect to the attr() expression and means something.  (Usually the 
coercion to "environment" happens automatically.)

The attr() expression is strongly deprecated and very much not 
guaranteed to work.  First, it's discouraged to use the .xData slot, 
which is part of the implementation and not part of the API.  And ditto 
to access _any_ slot by attr(), for the same reason.

However, in my experimenting the technique required xx$edit to have been 
evaluated at some point before the call to mtrace(). Reference methods 
are copied to the object when first required (for efficiency).  Because 
my workaround explicitly used xx$edit, the problem didn't arise.  Just 
evaluating xx$edit should be enough.

On the "before instantiated" point.  I assume you mean in order to trace 
the method in all objects generated from the reference class.  I had 
thought about that too.  The same mechanism I described in my previous 
mail works for this as well, but requires a kludge to get the 
environment containing the methods.  The steps I outlined are as before 
but modified (in the example) as follows:

 > mm =  mEditor$def at refMethods
 > edit = mm$edit
 > trace(edit, browser, where = mm)

(mm is the environment with the methods).  Then the objects generated by 
mEditor$new() will have the traced version.

The same technique didn't seem to work for mtrace(), but a modification 
might.

John


On 4/7/11 4:56 PM, Mark.Bravington at csiro.au wrote:
> 'mtrace' will work with reference classes, at least after an object is instantiated. I'm not familiar with the guts of reference classes, but the following quick experiment was successful.. If you run the example in '?ReferenceClasses' up to&  including this line :
>
> xx<- mEditor$new(data = xMat)
>
> and then do this:
>
> mtrace( edit, from=attr( xx, '.xData'))
>
> and then run the next line of the example, which is
>
> xx$edit(2, 2, 0)
>
> then the debug window will come up as normal.
>
> Now, what about if you want to mtrace 'edit' before objects are instantiated? Here the S4 structure defeated me temporarily, but I probably would have been able to beat it if I'd had more time... There are some notes on debugging S4 methods in 'package?debug' (note that '?mtrace' itself is out-of-date on S4-- I have gotten S4 debugging to work, but it's only described in 'package?debug') and that might be enough to get you going.
>
> HTH
>
> Mark ('debug' package author)
>
> Mark Bravington
> CSIRO CMIS
> Marine Lab
> Hobart
> Australia
> ________________________________________
> From: r-devel-bounces at r-project.org [r-devel-bounces at r-project.org] On Behalf Of A Zege [andre.zege at gmail.com]
> Sent: 08 April 2011 05:00
> To: r-devel at r-project.org
> Subject: [Rd] How to debug reference classes?
>
> How do you debug methods of a reference class? I've been using mtrace, which
> is excellent, but i cannot figure out how to mtrace a reference class
> method. Maybe there is some other way to debug these, for example with
> ordinary trace? for now i am only able to use options(error=recover), which
> is not giving me idea where exactly in the code i am once i am stopped on an
> error.
>
> --
> View this message in context: http://r.789695.n4.nabble.com/How-to-debug-reference-classes-tp3434269p3434269.html
> Sent from the R devel mailing list archive at Nabble.com.
>
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