[Swig-user] Default values broken in R

[Lauri L. <lau...@he...>]

Good new year,

I have a fuction called "reader" defined in struct called object in the 
swig file and I'm trying to %extend it as follows:

struct object {
     %extend {
         reader( char *filename, char *format="auto") { ... }
     }
};


This works at least for lua and Python. However in R the code that is 
generated looks like this:


SWIGEXPORT SEXP
R_swig_object_reader ( SEXP filename, SEXP format, SEXP s_swig_copy)
{
   struct region_set *result = 0 ;
   char *arg1 = (char *) 0 ;
   char *arg2 = (char *) "auto" ;
   unsigned int r_nprotect = 0;
   SEXP r_ans = R_NilValue ;
   VMAXTYPE r_vmax = vmaxget() ;

   arg1 = (char *)(SWIG_strdup(CHAR(STRING_ELT(filename, 0))));
   arg2 = (char *)(SWIG_strdup(CHAR(STRING_ELT(format, 0))));
   result = (struct region_set *)region_set_reader(arg1,arg2);
   r_ans = SWIG_R_NewPointerObj(SWIG_as_voidptr(result), 
SWIGTYPE_p_region_set, R_SWIG_EXTERNAL |  0 );
   free(arg1);
   free(arg2);
   vmaxset(r_vmax);
   if(r_nprotect)  Rf_unprotect(r_nprotect);

   return r_ans;
}


Clearly, the default value is not used, ever, even though it's resident 
in the C code. Moreover, when called from R, it demands an argument. So, 
the whole function definition has no default argument on R side.

 > r = object_reader("my_fancy_file")
Error in .class1(object) : argument "format" is missing, with no default
Calls: region_set_reader -> as -> .class1

On another note, there seems to be no %rcode which would be equivalent 
to %pythoncode and %rcode. Such thing would be very usable as well, not 
least to provide a working default argument version from R itself.

However even that doesn't fix the issue for member functions as they 
cannot be altered in R for the whole class.

A third issue I noticed is that returning an R_NilValue doesn't seem 
very simple from e.g. typemaps, as some code, somewhere, is trying to 
set attributes on the returned "object".

Any help/insight is appreciated.

  - Lauri