[Rcpp-devel] Rcpp and reference classes in R-2.12.0 and later

[Dominick Samperi]

On Mon, Nov 1, 2010 at 3:28 PM, Douglas Bates <bates at stat.wisc.edu> wrote:

> I should probably ask this question on R-devel as it is not directly
> an Rcpp question but the thread started here so ...
>
> I'm confused about accessor functions as described in
> help("setRefClass") under the argument "fields".  It states
>
>          The element in the list can alternatively be an _accessor
>          function_, a function of one argument that returns the field
>          if called with no argument or sets it to the value of the
>          argument otherwise. Accessor functions are used internally
>          ...
> The application I have in mind is classes of objects representing the
> response and auxiliary information in linear, generalized linear,
> nonlinear, and generalized nonlinear models.  An S4 implementation is
> in the MatrixModels package but the syntax of the update methods is
> awkward because they must replace slots then return the whole object,
> which can be rather large.  What I would like to do is have an update
> method that takes a new value of the linear predictor, updates the
> mean, the residuals, possibly the weights (for GLMs) and the weighted
> residuals.  After the update, methods for other objects can query the
> values of the weighted residuals, square root of the residual weights,
> square root of the X weights, etc.
>
> I'm trying to decide if the fields that can be queried should be
> declared as fields or as accessor functions.
>
> I haven't discovered any examples that declare accessor functions in
> the fields section.  Can anyone point out such an example to me?
>

Here is a trivial example (it does not use Rcpp). I cannot get
the methods = option to accept additional methods when I use
the accessors method, so this may be work in progress...

classxy <- setRefClass("myClass1",
                       fields = list(x='numeric',y='numeric'),
                       methods = classxy$accessors('x','y'))
classxy$methods()
foo = classxy$new()
foo$setX(3.14)
foo$getX()


>
> On Mon, Nov 1, 2010 at 10:44 AM, Romain Francois
> <romain at r-enthusiasts.com> wrote:
> > Le 01/11/10 16:34, Douglas Bates a écrit :
> >>
> >> On Mon, Nov 1, 2010 at 10:26 AM, Douglas Bates<bates at stat.wisc.edu>
> >>  wrote:
> >>>
> >>> What is a good place to start reading about using the newly installed
> >>> reference classes in R to interface with Rcpp?
> >>
> >> To answer my own question, the "Rcpp Modules" vignette.
> >
> > Perhaps it will be once we update the vignette. The content dates from
> > before we used reference classes.
> >
> > For reference classes themselves, the best place to look is
> > ?ReferenceClasses
> >
> > As Dirk pointed out, my chicago slides or our google slides might give
> > nuggets of information.
> >
> > I guess it also depends what specifically you want to learn about them.
> > Exposing a class is essentially the same as before reference classes.
> >
> > Deriving a C++ class, adding R methods to a class, etc ... is a new
> feature
> > we get for free with reference classes. This is not really Rcpp specific,
> so
> > maybe ?ReferenceClasses gives enough hints.
> >
> > Romain
> >
> > --
> > Romain Francois
> > Professional R Enthusiast
> > +33(0) 6 28 91 30 30
> > http://romainfrancois.blog.free.fr
> > |- http://bit.ly/czHPM7 : Rcpp Google tech talk on youtube
> > |- http://bit.ly/9P0eF9 : Google slides
> > `- http://bit.ly/cVPjPe : Chicago R Meetup slides
> >
> >
> > _______________________________________________
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> >
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