[Rcpp-devel] Extract a function from a list and create a call

[Romain Francois]

Le 22/03/10 03:12, Douglas Bates a écrit :
> On Sat, Mar 20, 2010 at 2:53 AM, Romain Francois
> <romain at r-enthusiasts.com>  wrote:
>>
>> Hello,
>>
>> The issue with CharacterVector is that the proxy classes :
>> "string_name_proxy" and "string_proxy" only have implicit conversion to SEXP
>> and char* :
>>
>> operator char* (){
>>         return get() ;
>> }
>> operator SEXP(){
>>         return ::Rf_mkString(get()) ;
>> }
>>
>> i.e. they don't have implicit conversion to std::string. We can't have both
>> implicit conversions to char* and std::string because it causes ambiguities
>> and the compiler is much unhappy.
>>
>> So given a CharacterVector, we can grab the first element as a std::string
>> using one of these options:
>>
>> require( Rcpp )
>> require( inline )
>>
>> fx<- cfunction( signature( x_ = "character" ), '
>> CharacterVector x(x_);
>>
>> // x[0] is implicitely converted to a char* and the string( char*)
>> // constructor is used
>> std::string y( x[0] ) ;
>>
>> // using string::operator=( char* ) with a std::string created before
>> std::string z ;
>> z = x[0] ;
>>
>> // but this does not work
>> // std::string foo = x[0] ;
>> // because there is no implicit conversion proxy ->  std::string
>>
>> ', Rcpp = TRUE, includes = "using namespace Rcpp;" )
>
> I can run your example without a problem but when I try to go to the
> next stage and extract the character vectors from a list, it seems
> that internally the conversion to a STRSXP has not been completed (or
> something like that).  Attempts to extract the first string from the
> CharacterVector extracted by name from the list fail with an error
> message of
>> fx(binomial())
> Assigned fam of length 1, llink of length 1
> Error in fx(binomial()) :
>    STRING_ELT() can only be applied to a 'character vector', not a 'symbol'

This is worrying. Not sure where the problem is yet.

And when I run the code on OSX (gcc 4.2), I get :

  *** caught segfault ***
address 0x0, cause 'memory not mapped'

Traceback:
  1: .Call("file10d63af1", PACKAGE = f, l)
  2: fx(binomial())
aborting ...
Segmentation fault

which is not good either.


> The test script is
>
> suppressWarnings(require(inline))
> suppressWarnings(require(Rcpp))
>
> fx<- cfunction( signature( l = "list" ), '
>      List ll(l);
>      CharacterVector fam = ll["family"], llink = ll["link"];
>      Rprintf("Assigned fam of length %d, llink of length %d\\n",
> 	    fam.size(), llink.size());
>      char *fpt = (char *)0, *lpt = (char *)0;
>      if (fam.size()) fpt = fam[0];
>      if (llink.size()) lpt = llink[0];
>      return List::create(_["fam"] = std::string(fpt),
>                          _["llink"] = std::string(lpt));
> ', Rcpp = TRUE, includes = "using namespace Rcpp;" )
>
> fx(binomial())
> fx(gaussian())
> fx(poisson())

-- 
Romain Francois
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http://romainfrancois.blog.free.fr
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