[Rcpp-devel] Pass an Rcpp module object to a method belonging to another module from R?

[Hao Ye]

Grant,

In my own work, I found that input validation is actually significantly
easier to do in R. (and even if you did do it in the c++ layer, informative
error messages should probably be thrown as exceptions back to R,
regardless.)

A giant constructor is not necessary either, as you can send data and
arguments to the c++ class through separate functions. This gives you some
flexibility if, say, you wanted to write different R wrapper functions
using the same underlying computational object.

My assumption, based on your original email, was that you were looking for
a use case where you might want to call separate computations on different
objects of class A from R (thus necessitating exposing A's functions to R),
but then also be able to do some computations in an object of class B that
could swap different objects of class A in and out. If that isn't the case,
then there's probably a simpler, if less elegant, implementation to do what
you want.

Best,
--
Hao Ye
hye at ucsd.edu

On Tue, Sep 9, 2014 at 6:47 PM, Grant Brown <grant.brown73 at gmail.com> wrote:

> Thanks for the feedback, I'll definitely consider those options.
>
> My original motivation (besides the sheer convenience of Rcpp modules as a
> way to move work into C++ land) was that there's a lot of data and model
> specification information that needs to migrate from R user land to the
> lower level library, and I didn't want the main model object to have to
> keep track of too much state (or have too huge of a constructor).
>
> My fallback should this prove unfeasible will probably be to put  together
> an R layer which can collect and validate the requisite components before
> providing them to the giant constructor.
>
> Thanks!
>
>
>
> On Tue, Sep 9, 2014 at 8:16 PM, Dirk Eddelbuettel <edd at debian.org> wrote:
>
>>
>> On 9 September 2014 at 19:56, Grant Brown wrote:
>> | Hi folks,
>> |
>> | I'm building several Rcpp modules which specify parts of a complicated
>> | statistical model, and want to pass them to a main module for use. Is
>> there an
>> | easy way to do this?
>> |
>> | Below is a simplified example, with question marks where I'm not sure
>> what to
>> | do. I've tried accepting a pointer to A, playing with using XPtrs, and
>> a bunch
>> | of things which made far less sense, but so far no luck.
>> |
>> | Any suggestions or links to sections of the docs I should revisit would
>> be
>> | appreciated.
>>
>> That's neat and somewhat ambitious. Not sure it can be done; Romain may
>> have
>> pointers for you.
>>
>> I prefer to keep things simple; at least initially.  I sometimes create a
>> larger class (possibly as a singleton) and then have accessors from R
>> which
>> initialize, supply parameters, alter parameters, request computation, ...
>> You
>> can then play with factories, and components, and inheritance, etc pp.
>>
>> By keeping the interface simple I can set it up in a way which lets me
>> test
>> the functionality also in a simple main away from R.  But that may just
>> be me.
>>
>> Dirk
>>
>>
>> | Thanks,
>> | -Grant
>> |
>> |
>> | ## file: A.cpp
>> |
>> | class A
>> | {
>> | public:
>> | A();
>> | ~A();
>> | };
>> |
>> | class B
>> | {
>> | public:
>> | B();
>> | void DoSomethingWithInstanceOfA(???);
>> | ~B();
>> | };
>> |
>> | A::A()
>> | {
>> | // Do stuff
>> | }
>> |
>> | B::B()
>> | {
>> | // Do stuff
>> | }
>> |
>> | B::DoSomethingWithInstanceOfA(???)
>> | {
>> | // Do stuff
>> | }
>> |
>> | RCPP_MODULE(mod_A)
>> | {
>> | using namespace Rcpp;
>> | class_<A>( "A" )
>> | .constructor();
>> | }
>> |
>> | RCPP_MODULE(mod_B)
>> | {
>> | using namespace Rcpp;
>> | class_<B>( "B" )
>> | .constructor()
>> | .method("DoSomethingWithInstanceOfA", &B::DoSomethingWithInstanceOfA);
>> | }
>> |
>> |
>> | ### End pseduo c++ code
>> |
>> |
>> | _______________________________________________
>> | Rcpp-devel mailing list
>> | Rcpp-devel at lists.r-forge.r-project.org
>> | https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/rcpp-devel
>>
>> --
>> http://dirk.eddelbuettel.com | @eddelbuettel | edd at debian.org
>>
>
>
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