[Rcpp-devel] How to give default value with Rcpp and roxygen2 involving seq_len

[Dirk Eddelbuettel]

On 13 January 2016 at 16:41, Lafaye de Micheaux Pierre wrote:
| Hello everybody,
| 
| Let's consider the simple function:
| 
| f <- function(x = 1:10) {return(x)}
| 
| where the argument 'x' could take non integer values.
| 
| I would like to create such a function using Rcpp and roxygen2. If I try
| something like:
| 
| //' @param x Vector of real values
| NumericVector f(NumericVector x) {return(x);}
| 
| then after creation using devtools, I will obtain a function like this
| one:
| f <- function(x) {return(x)}
| 
| How can I write things in my C++ code so that I will obtain 
| the x = 1:10 default values?
| 
| I tried something like:
|  //' @param x Vector of real values
| NumericVector f(NumericVector x = NumericVector::create(seq_len(10))
| {return(x);}
| 
| but it failed completely ...
| 
| I am quite new to Rcpp, so I apologize if my question is too naive. If
| this is the case, feel free to send me a web link to some documentation
| that I could learn to try to solve this problem by myself.

I am sure I have more examples by one quick check lead to RcppApt where I do

   //' The APT Package Management system uses a data-rich caching 
   //' structure. This accessor function returns the names of installable
   //' packages for a given regular expression.
   //'
   //' @title Retrieve Names of All Installable Packages
   //' @param regexp Regular expression for package name
   //' @return A data frame with columns containing the 
   //' package name, the installed version (or NA if not installed)  
   //' and the section it is installed in (or NA).
   //' @author Dirk Eddelbuettel
   //' @examples 
   //' getPackages("^r-(base|doc)-")
   // [[Rcpp::export]]
   Rcpp::DataFrame getPackages(const std::string regexp = ".") {

   ...

See https://github.com/eddelbuettel/rcppapt


What you have above is one-level tricker as it uses Rcpp constructs. I am not
sure I tried that.  I most just initialized standard C++ types: bool, string, ...

Dirk

-- 
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