[Rcpp-devel] check validity of object created from Rcpp module

[Dirk Eddelbuettel]

On 26 June 2012 at 17:21, Jiqiang Guo wrote:
| Dear List,
| 
| I am wondering if there is a way to check whether an object created from Rcpp's
| module is valid or not especially for objects loaded in another session. 
| 
| In detail, we know that we could not save and load objects created from Rcpp's
| module [section 5 of http://cran.r-project.org/web/packages/Rcpp/vignettes/
| Rcpp-modules.pdf].  But that does not prevent users doing that. So if an
| object created from Rcpp's module is loaded in another session, we would end up
| with errors or even segfault.  It would be nice we have a method to check if
| it is valid or not so that when we are writing a package, we could do a check
| before calling those methods of that object.  

It's a very good idea. I don't have a good idea as to how we'd do this though.

Dirk
 
| An illustrative example:
| 
| require("Rcpp")
| require("inline")
| 
| inc <- '
| class Foo {
| private:
|   int x_;
| public:
|   Foo(int x) : x_(x) { }
|   int getx() const { return x_;}
| }; 
| 
| RCPP_MODULE(foo) {
|   class_<Foo>("Foo")
|   .constructor<int>() 
|   .method("getx", &Foo::getx) 
|   ;
| }
| 
| fx <- cxxfunction(signature(), "", include = inc, plugin = "Rcpp", verbose =
| FALSE)
| m <- Module("foo", getDynLib(fx))
| cppo  = new(m$Foo, 5)
| 
| print(cppo$getx())
| save("cppo", file = 'cppo.RData')
| 
| rm(list = ls())
| load("cppo.RData")
| print(cppo$getx())
| 
| For the above code, we know the last line would not work.  If we have a
| function to test the validity of cppo,then if not valid, we would not call
| cppo's function and are able to tell users that cppo is not valid any more. 
| 
| Best,
| Jiqiang 
| 
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-- 
Dirk Eddelbuettel | edd at debian.org | http://dirk.eddelbuettel.com