Putting initial values into an R6 Singleton - r

Question

I would like to store initial values in a Singleton in R, so I am using the R6 Singleton class. The examples show how to manipulate internal variables, but I cannot find a way to pass in values. I tried
library( R6 )
library( R6P )
Parameters <- R6::R6Class("Parameters", inherit = R6P::Singleton, public = list(
elements = NA,
initialize = function(...) { tmp<-list(...);if (length(tmp)>0) {self$elements<-tmp} },
retrieve = function(){ self$elements }
))
My goal is that if I create one instance with initial values, then subsequent instances will find the same value. When I run the above, however, I get:
> p <- Parameters$new( "a" )
> p$retrieve()
[[1]]
[1] "a"
> q <- Parameters$new()
> q$retrieve()
[1] NA
How can I get the second instance of the Singleton, q, to return the initialized value "a"?
------ Edited using #eduardokapp suggestion -------
(First, I don't know enough about SO rules to know whether to post an edit, post my own answer or ask a new question so I chose to edit the initial question. Apologies if that is wrong.)
Looking at the link to Hadley Wickham's "Advanced R" chapter, this edit gives me the same object in the "elements" variable like a Singleton:
library( pryr )
library( R6 )
library( R6P )
TemporaryFile <- R6Class("TemporaryFile", list(
path = NULL,
initialize = function(...) {
self$path <- list(...)
},
finalize = function() {
message("Cleaning up ", self$path)
unlink(self$path)
}
))
Parameters <- R6::R6Class("Parameters", inherit = R6P::Singleton, public = list(
name = NULL,
elements = TemporaryFile$new(),
initialize = function(name) { self$name = name },
retrieve = function(){ address(elements) }
))
which when I run gives:
> p <- Parameters$new( "a" )
> q <- Parameters$new( "b" )
> p$name
[1] "a"
> q$name
[1] "b"
> p$retrieve() == q$retrieve()
[1] TRUE
>
The problem now is how to assign an input value in "TemporaryFile$new()". Anything I try to put in ("path","...") gives an error. How do you assign a value to the internal class so that you can store a value on the first instantiation that will be shared by all subsequent instantiations? Am I just making this more complicated than it needs to be?

Answer 1

Two tricks. The first was to set the preserved value after construction of the instance. The second was to use an 'ifelse' function when assigning the preserved 'value'. Otherwise, it is written over at construction.
library( R6 )
library( R6P )
Parameters <- R6::R6Class("Parameters", inherit = R6P::Singleton, public = list(
input = NA,
value = ifelse( exists("self$value"), value, NA ),
assign = function(input) {self$value = input}
))
Test
> library(pry)
> p <- Parameters$new()
> p$assign(input="Hi")
> p$value
[1] "Hi"
> q <- Parameters$new()
> q$value
[1] "Hi"
> p$value
[1] "Hi"
> identical(address(p),address(q))
[1] TRUE
Every new instance of Parameters will hold the same 'value'.