I am trying to create a R package mypckg with a function createShinyApp. The latter function should create a directory structure ready to use as shiny app at some location. In this newly created shiny app, I have some variables, which should be accessed from within the shiny app, but not by the user directly (to prevent a user from accidentally overwriting them). The reason for these variables to exist (I know one should not use global variables) is that the shiny app is treating a text corpus and I want to avoid passing (and hence copying) it between the many functions because this could lead to exhaustion of the memory. Somebody using mypckg should be able to set these variables and later use createShinyApp.
My ideas so far are:
mypckg::createShinyApp save the protected variables in a protectedVariables.rds file and get the shinyApp to load the variables from this file into a new environment. I am not very experienced with environments so I could not get this to work properly yet because the creation of a new environment is not working upon running a shiny app so far.mypckg::createShinyApp save the protected variables in a protectedVariables.rds file and get the shinyApp to load the variables from this file into the options. Thereafter I would access the variables and set the variables with options() and getOption.What are the advantages and disadvantages of these ideas and are there yet simpler and more elegant ways of achieving my goal?
It's a little bit difficult to understand the situation without seeing a concrete example of the kind of variable and context you're using it in, but I'll try to answer.
First of all: In R, it's very very difficult to achieve 100% protection of a variable. Even in shiny, the authors of shiny tried putting up a lot of mechanisms to disallow some variables from getting overwritten by users (like the input variable for example), and while it does make it much harder, you should know that it's impossible, or at least extremely difficult, to actually block all ways of changing a variable.
With that disclaimer out of the way, I assume that you'd be happy with something that prevents people from accidentally overwriting the variable, but if they go purposely out of their way to do it, then so be it. In that case, you can certainly read the variables from an RDS file like you suggest (with the caveat that the user can of course overwrite that file). You can also use a global package-level variable -- usually talking about global variables is bad, but in the context of a package it's a very common thing to do.
For example, you can define in a globals.R file in your package:
.mypkgenv <- new.env(parent = emptyenv())
.mypkgenv$var1 <- "some variable"
.mypkgenv$var2 <- "some other variable"
And the shiny app can access these using
mypckg:::.mypkgenv$var1
This is just one way, there are other ways too