[Rcpp-devel] passing function

Davor Cubranic cubranic at stat.ubc.ca
Wed Jan 26 17:30:48 CET 2011


On 2011-01-26, at 7:38 AM, Dirk Eddelbuettel wrote:

> cpp <- '
> 	int n = as<int>(N);
> 	NumericVector numvec(xvec) ;
> 	Function f(fun) ;
> 	for( int i=0; i<n; i++){
> 		numvec = f( numvec ) ;
> 	}
> 	return numvec ;
> '
> 
> # create a C++ function
> funx <- cfunction(signature(N = "integer" , xvec = "numeric", fun = "function" ),
>                  cpp, , Rcpp = TRUE, include = "using namespace Rcpp; ")
[...]
> Now for your questions:
> 
>    I see that f is a Function object but what is fun? 
> 
> There is no 'fun' but 'funx' is an R function created by cfunction() [ of the
> inline package ] containing executable code created by cfunction() from the
> source code submitted via variable 'cpp'.

I think the question was about the line 'Function f(fun)'. 

And the answer is that 'fun' is the second argument of the C++ function, and is an SEXP for the R function passed in. (See the 'signature' call in assignment to 'funx'.) So 'Function f(fun)' creates an instance of Rcpp::Function called 'f' out of the 'fun' SEXP.

Davor



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