Accessing private closure in R package

env_fxn_example.R

# Goal: To have a function that package users can call to set a variable that
# will be used to create a closure. The problem with the "problem" code
# is that it exposes the created function (private_function) to the user inappropriately.

############################ Problem

# a function in my package
user_calls <- function(string){
  private_function <<- function(){
    print(string)
  }
}

# another function in my package
pkg_function <- function(){
  private_function()
}

# user should be able to do
user_calls("kittens")
pkg_function()

# user should not be able to do
private_function()

############################ Solution

envex <- new.env()

user_calls <- function(string){
  assign("private_function", function(){ print(string) }, envir = envex)
}

pkg_function <- function(){
  envex$private_function()
}

user_calls("kittens")
pkg_function()