Explicit Rcpp:: in the initalize method for C++ classes wrapped inside modules

[riccardoporreca]

Otherwise the Rcpp functions are unknown when objects are initialized, unless Rcpp is attached.

inc <- '
class World {
public:
    World() {};
    std::string greet() { return "hello"; };

};
RCPP_MODULE(yada){
    using namespace Rcpp ;
    class_<World>("World")
    .constructor()
    .method("greet", &World::greet)
    ;
}
'
fx <- inline::cxxfunction(signature(), plugin = "Rcpp", include = inc)
yada <- Rcpp::Module("yada", inline::getDynLib(fx))
new(yada$World)$greet()
#> Error in cpp_object_initializer(.self, .refClassDef, ...): could not find function "cpp_object_initializer"
library(Rcpp)
new(yada$World)$greet()
#> [1] "hello"

^{Created on 2019-07-21 by the reprex package (v0.3.0)}

Session info

devtools::session_info()
#> ─ Session info ──────────────────────────────────────────────────────────
#>  setting  value                       
#>  version  R version 3.6.1 (2019-07-05)
#>  os       Ubuntu 18.04.2 LTS          
#>  system   x86_64, linux-gnu           
#>  ui       X11                         
#>  language (EN)                        
#>  collate  en_US.UTF-8                 
#>  ctype    en_US.UTF-8                 
#>  tz       Europe/Zurich               
#>  date     2019-07-21                  
#> 
#> ─ Packages ──────────────────────────────────────────────────────────────
#>  package     * version date       lib source                        
#>  assertthat    0.2.1   2019-03-21 [1] CRAN (R 3.6.0)                
#>  backports     1.1.4   2019-04-10 [1] CRAN (R 3.6.0)                
#>  callr         3.3.1   2019-07-18 [1] CRAN (R 3.6.1)                
#>  cli           1.1.0   2019-03-19 [1] CRAN (R 3.6.0)                
#>  codetools     0.2-16  2018-12-24 [4] CRAN (R 3.5.2)                
#>  crayon        1.3.4   2017-09-16 [1] CRAN (R 3.6.0)                
#>  desc          1.2.0   2018-05-01 [1] CRAN (R 3.6.0)                
#>  devtools      2.1.0   2019-07-06 [1] CRAN (R 3.6.1)                
#>  digest        0.6.20  2019-07-04 [1] CRAN (R 3.6.1)                
#>  evaluate      0.14    2019-05-28 [1] CRAN (R 3.6.0)                
#>  fs            1.3.1   2019-05-06 [1] CRAN (R 3.6.0)                
#>  glue          1.3.1   2019-03-12 [1] CRAN (R 3.6.0)                
#>  highr         0.8     2019-03-20 [1] CRAN (R 3.6.0)                
#>  htmltools     0.3.6   2017-04-28 [1] CRAN (R 3.6.0)                
#>  inline        0.3.15  2018-05-18 [1] CRAN (R 3.6.1)                
#>  knitr         1.23    2019-05-18 [1] CRAN (R 3.6.1)                
#>  magrittr      1.5     2014-11-22 [1] CRAN (R 3.6.0)                
#>  memoise       1.1.0   2017-04-21 [1] CRAN (R 3.6.0)                
#>  pkgbuild      1.0.3   2019-03-20 [1] CRAN (R 3.6.0)                
#>  pkgload       1.0.2   2018-10-29 [1] CRAN (R 3.6.0)                
#>  prettyunits   1.0.2   2015-07-13 [1] CRAN (R 3.6.0)                
#>  processx      3.4.1   2019-07-18 [1] CRAN (R 3.6.1)                
#>  ps            1.3.0   2018-12-21 [1] CRAN (R 3.6.0)                
#>  R6            2.4.0   2019-02-14 [1] CRAN (R 3.6.0)                
#>  Rcpp        * 1.0.2   2019-07-21 [1] Github (RcppCore/Rcpp@84c787f)
#>  remotes       2.1.0   2019-06-24 [1] CRAN (R 3.6.0)                
#>  rlang         0.4.0   2019-06-25 [1] CRAN (R 3.6.0)                
#>  rmarkdown     1.14    2019-07-12 [1] CRAN (R 3.6.1)                
#>  rprojroot     1.3-2   2018-01-03 [1] CRAN (R 3.6.0)                
#>  sessioninfo   1.1.1   2018-11-05 [1] CRAN (R 3.6.0)                
#>  stringi       1.4.3   2019-03-12 [1] CRAN (R 3.6.0)                
#>  stringr       1.4.0   2019-02-10 [1] CRAN (R 3.6.0)                
#>  testthat      2.1.1   2019-04-23 [1] CRAN (R 3.6.0)                
#>  usethis       1.5.1   2019-07-04 [1] CRAN (R 3.6.0)                
#>  withr         2.1.2   2018-03-15 [1] CRAN (R 3.6.0)                
#>  xfun          0.8     2019-06-25 [1] CRAN (R 3.6.0)                
#>  yaml          2.2.0   2018-07-25 [1] CRAN (R 3.6.0)                
#> 
#> [1] /home/mirai/R/x86_64-pc-linux-gnu-library/3.6
#> [2] /usr/local/lib/R/site-library
#> [3] /usr/lib/R/site-library
#> [4] /usr/lib/R/library

This occurs when modules are created explicitly via Module(), both inline (see above) and in packages. The latter case can be seen e.g. using Rcpp.package.skeleton() and replacing loadModule("yada", TRUE) with yada <- Module("yada") and running new(yada$World)$greet() after installing and loading the package.
This not an issue for the common case of using loadModule() in packages, where typically import(Rcpp) is in the NAMESPACE, otherwise we would observe the same behavior.

The effectiveness of using Rcpp:: can be tested by re-running the example above after intalling Rcpp from the branch

remotes::install_github("riccardoporreca/Rcpp", "fix-module-initialize")

The object can now be created even prior to Rcpp being attached.

[eddelbuettel]

That looks rather useful. I'll try to look into it later today.

[kevinushey]

LGTM!