[Rcpp-devel] Rcpp modules

[Dirk Eddelbuettel]

On 19 May 2010 at 15:07, Romain Francois wrote:
| One thing perhaps I'd like opinions about is the use if the name 
| "function" in :
| 
| RCPP_MODULE(yada){
| 	using namespace Rcpp ;
| 	function( "hello" , &hello ) ;
| }
| 
| Boost.Python uses "def" but this is too pythonic for me. OTOH, having 
| both Rcpp::Function (the class that deals with R functions) and 
| Rcpp::function (for the module code) might be confusing.
| 
| Any suggestion ? Maybe Rcpp::fun ? Or should I use some other namespace 
| for this functionality ?

Tough one. I also think that maybe 'function' is iffy. That said, it is not a
keyword at the C++ language level (!!) so maybe even mingw will be kind to us
(inside joke alert here).  Maybe 'Function' just to show it is different?
But that is odd too.  Maybe   f(...)   in tip-of-the hat to math?

Maybe start with function. The option of later wrapping it into a
sub-namespace or its own namespace is good too.

Dirk
 
| Romain
| 
| Le 19/05/10 12:09, Romain Francois a écrit :
| >
| > Hello,
| >
| > I've been looking at Boost.Python lately and thought we might be able to
| > port some of the ideas to Rcpp too.
| >
| >
| > I commited (rev 1281) some code to Rcpp that introduces the notion of
| > Rcpp modules (wording might change later). A module is a collection of
| > C++ functions that :
| > - take 0 or more parameters of arbitrary type, not really arbitrary but
| > anything that Rcpp::as can deal with
| > - returns void or any type that Rcpp::wrap can handle
| >
| >
| > Here is an example of C++ code using the concept of Rcpp module :
| >
| > std::string hello(){
| > return "hello" ;
| > }
| >
| > int bar( int x){
| > return x*2 ;
| > }
| >
| > double foo( int x, double y){
| > return x * y ;
| > }
| >
| > void bla( ){
| > Rprintf( "hello\\n" ) ;
| > }
| >
| > void bla1( int x){
| > Rprintf( "hello (x = %d)\\n", x ) ;
| > }
| >
| > void bla2( int x, double y){
| > Rprintf( "hello (x = %d, y = %5.2f)\\n", x, y ) ;
| > }
| >
| >
| > RCPP_MODULE(yada){
| > using namespace Rcpp ;
| >
| > function( "hello" , &hello ) ;
| > function( "bar" , &bar ) ;
| > function( "foo" , &foo ) ;
| > function( "bla" , &bla ) ;
| > function( "bla1" , &bla1 ) ;
| > function( "bla2" , &bla2 ) ;
| >
| > }
| >
| > All the magic happens because the compiler knows how to distinguish the
| > type of each function pointer and we manage to intercept this
| > information through C++ templates.
| >
| > The only price to pay is the declarative call to the RCPP_MODULE macro.
| >
| >
| > On the R side, we just pick it up using the Module function in Rcpp :
| >
| >  > # inc is the code above
| >  > fx <- cppfunction( signature(), "", include = inc )
| >  >
| >  > # look for the Module called "yada" in the DLL we just compiled
| >  > yada <- Module( "yada", getDLL( fx ) )
| >  > print( yada )
| > Rcpp module 'yada'
| > 6 functions:
| > bar : 1 arguments
| > bla : 0 arguments
| > bla1 : 1 arguments
| > bla2 : 2 arguments
| > foo : 2 arguments
| > hello : 0 arguments
| >  >
| >  > print( yada$hello() )
| > [1] "hello"
| >  > print( yada$bar( 2L ) )
| > [1] 4
| >  > print( yada$foo( 2L, 4.0 ) )
| > [1] 8
| >  > yada$bla()
| > hello
| >  > yada$bla1( 2L )
| > hello (x = 2)
| >  > yada$bla2( 2L, 5 )
| > hello (x = 2, y = 5.00)
| >
| >
| >
| > Right now, this is limited to a maximum of 2 parameters because I wrote
| > this manually, but once I make some R code to generate the template
| > code, we should be able to get up to 65 parameters (same as .Call)
| 
| Done !
| 
| > functions are only the tip of boost.python iceberg, obviously we also
| > want to expose C++ classes the way boost.python does, but this might be
| > slightly more involved.
| >
| >
| > Romain
| >
| 
| 
| -- 
| Romain Francois
| Professional R Enthusiast
| +33(0) 6 28 91 30 30
| http://romainfrancois.blog.free.fr
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-- 
  Regards, Dirk