How to define "hidden global variables" inside R packages?

Question

I have the following 2 functions in R:

exs.time.start<-function(){
  exs.time<<-proc.time()[3]
  return(invisible(NULL))
}

exs.time.stop<-function(restartTimer=TRUE){
  if(exists('exs.time')==FALSE){
    stop("ERROR: exs.time was not found! Start timer with ex.time.start")
  }
  returnValue=proc.time()[3]-exs.time
  if(restartTimer==TRUE){
    exs.time<<-proc.time()[3]
  }
  message(paste0("INFO: Elapsed time ",returnValue, " seconds!"))
  return(invisible(returnValue))
}

The function exs.time.start creates a global variable (exs.time) with the CPU time of the moment when I called the function.

The function exs.time.stop access that global variable and return the time between the execution of exs.time.start and exs.time.stop.

My objective is to create a package in R with these two functions. How can I define that global variable (exs.time) to be a variable that's invisible to the user, so he couldn't see this variable in the R Global Environment?

Can I define this variable to be a "hidden" global variable inside the R package environment/namespace?

It's my first time working with packages, so I don't know exactly how to use very well the namespace file when defining packages. I'm creating my package using R Studio and Roxygen2.

Any help or suggestion would be great!

Renan Vilas Novas Renan Vilas Novas · Accepted Answer · 2015-12-13T19:44:58

Thank you for sharing your packages @Dirk Eddelbuettel

The solution for my question is the following:

.pkgglobalenv <- new.env(parent=emptyenv())

exs.time.start<-function(){
  assign("exs.time", proc.time()[3], envir=.pkgglobalenv)
  return(invisible(NULL))
}

exs.time.stop<-function(restartTimer=TRUE){
  if(exists('exs.time',envir=.pkgglobalenv)==FALSE){
    stop("ERROR: exs.time was not found! Start timer with exs.time.start")
  }
  returnValue=proc.time()[3]-.pkgglobalenv$exs.time
  if(restartTimer==TRUE){
    assign("exs.time", proc.time()[3], envir=.pkgglobalenv)
  }
  message(paste0("INFO: Elapsed time ",returnValue, " seconds!"))
  return(invisible(returnValue))
}

I've created an environment with new.env(), inside my R file, before my function definitions.
I've used assign() to access the environment and change the value of my global variable!

The variable is hidden and everything works fine! Thanks guys!

How to define "hidden global variables" inside R packages?

2 Answers