Using reactiveValues across multiple modules in R Shiny

I'm trying to use reactiveValues across multiple modules in an R shiny app.

I have set up an example to illustrate my problem. It consists of a main application containing a reactiveValue which is a data frame of 3 columns and 3 modules designed to "read", "write" and "read and write" the reactiveValue.

• Read: Application -> Module
• Write: Module -> Application
• Read and Write: Application <-> Module

I get the error:

Warning: Error in <-: object of type 'closure' is not subsettable

Note that the code works if the reactiveValue is just a simple variable e.g. integer, but not with a data frame where components need to be updated rather than the whole data frame.

I have found the following link very useful. Not sure if it covers my case. https://www.ardata.fr/en/post/2019/04/26/share-reactive-among-shiny-modules/

Any ideas on how to solve this problem?

Here is my code:

library(shinydashboard)

readUI <- function(id, label = "Read") {

  ns <- NS(id)

  tagList(
    valueBoxOutput(ns("showX"))
  )
}

read <- function(input, output, session, x) {

  ns <- session$ns

  output$showX <- renderValueBox({
    valueBox(x(), "x")
  })

}

writeUI <- function(id, label = "Write") {

  ns <- NS(id)

  tagList(
    selectizeInput(ns("selectX"), "Select a value for x", choices = 1:10),
    actionButton(ns("submit"), "Submit")
  )
}

write <- function(input, output, session) {

  ns <- session$ns

  toReturn <- reactiveValues(x = data.frame(a=c(1), b=c(2), c=c(3)), trigger = NULL)

  observeEvent(input$submit, {
    toReturn$x$a <- as.numeric(input$selectX)
    toReturn$trigger <- toReturn$trigger + 1
  })

  return(toReturn)

}

readAndWriteUI <- function(id, label = "ReadAndWrite") {

  ns <- NS(id)

  tagList(
    valueBoxOutput(ns("showX")),
    selectizeInput(ns("selectX"), "Select a value for x", choices = 1:10),
    actionButton(ns("submit"), "Submit")
  )

}

readAndWrite <- function(input, output, session, x) {

  ns <- session$ns

  toReturn <- reactiveValues(x = x, trigger = NULL)

  output$showX <- renderValueBox({
    valueBox(x(), "x")
  })

  observeEvent(input$submit, {
    toReturn$x$a <- as.numeric(input$selectX)
    toReturn$trigger <- toReturn$trigger + 1
  })

  return(toReturn)

}

ui <- dashboardPage(

  dashboardHeader(title = "Example"),

  dashboardSidebar(),

  dashboardBody(
    tabsetPanel(id = "mainTabSetPanel",
      tabPanel("Read", readUI("Read")),
      tabPanel("Write", writeUI("Write")),
      tabPanel("ReadAndWrite", readAndWriteUI("ReadAndWrite"))
    )
  )
)

server <- function(input, output, session) {

  rv <- reactiveValues(x = data.frame(a=c(1), b=c(2), c=c(3)))

  callModule(read, "Read", reactive(rv$x))
  output_Write <- callModule(write, "Write")
  output_ReadAndWrite <- callModule(readAndWrite, "ReadAndWrite", reactive(rv$x))

  observeEvent(output_Write$trigger, {
    print("Updating x from Write")
    rv$x <- output_Write$x
    #updateTabsetPanel(session, "mainTabSetPanel", selected = "Read")
  })

  observeEvent(output_ReadAndWrite$trigger, {
    print("Updating x from ReadAndWrite")
    rv$x <- output_ReadAndWrite$x
    #updateTabsetPanel(session, "mainTabSetPanel", selected = "Read")
  })
}

shinyApp(ui, server)