I am learning to use R6 in a Shiny app with the aim of separating the logic from the app.

I have a question about the value of the initialize function in the R6 class.

As shown in the reproducible example below, I have defined name = 'Eric' and set up the initialize function to assign ‘Eric’ as the default value of name. Why is ‘Eric’ not displayed when the app is launched?

library(shiny)
library(R6)
library(gargoyle)

# R6 object -----------------------------------------------------------------------------

ExampleR6 <- R6Class(
  classname = "example", 
  public    = list(
    name       = "Eric",
    initialize = \(name = "Eric") {
      self$name <- name
    }
  ))


# Module 1 ------------------------------------------------------------------------------

mod_1_UI <- function(id) {
  ns <- NS(id)
  tagList(
    textInput(inputId = ns("input_name"), label = "What's your name?")
  )
}

mod_1_Server <- function(id, r6) {
  moduleServer(
    id,
    function(input, output, session) {
      
      observeEvent(input$input_name, {
        
        r6$name <- input$input_name
        
        trigger("change_name")
      })
    }
  )
}


# Module 2 ------------------------------------------------------------------------------

mod_2_UI <- function(id) {
  ns <- NS(id)
  tagList(
    textOutput(outputId = ns("output_name"))
  )
}

mod_2_Server <- function(id, r6) {
  moduleServer(
    id,
    function(input, output, session) {
      
      observeEvent(watch("change_name"), {
        
        output$output_name <- renderText(r6$name)
      })
    }
  )
}


# Main app ------------------------------------------------------------------------------


ui <- fluidPage(
  
  mod_1_UI(id = "mod_1"),
  mod_2_UI(id = "mod_2")
)

server <- function(input, output, session) {
  
  hello_r6 <- ExampleR6$new()
  
 init("change_name")
  
  mod_1_Server(id = "mod_1", r6 = hello_r6)
  mod_2_Server(id = "mod_2", r6 = hello_r6)
}

shinyApp(ui, server)

I am learning to use R6 in a Shiny app with the aim of separating the logic from the app.

I have a question about the value of the initialize function in the R6 class.

As shown in the reproducible example below, I have defined name = 'Eric' and set up the initialize function to assign ‘Eric’ as the default value of name. Why is ‘Eric’ not displayed when the app is launched?

library(shiny)
library(R6)
library(gargoyle)

# R6 object -----------------------------------------------------------------------------

ExampleR6 <- R6Class(
  classname = "example", 
  public    = list(
    name       = "Eric",
    initialize = \(name = "Eric") {
      self$name <- name
    }
  ))


# Module 1 ------------------------------------------------------------------------------

mod_1_UI <- function(id) {
  ns <- NS(id)
  tagList(
    textInput(inputId = ns("input_name"), label = "What's your name?")
  )
}

mod_1_Server <- function(id, r6) {
  moduleServer(
    id,
    function(input, output, session) {
      
      observeEvent(input$input_name, {
        
        r6$name <- input$input_name
        
        trigger("change_name")
      })
    }
  )
}


# Module 2 ------------------------------------------------------------------------------

mod_2_UI <- function(id) {
  ns <- NS(id)
  tagList(
    textOutput(outputId = ns("output_name"))
  )
}

mod_2_Server <- function(id, r6) {
  moduleServer(
    id,
    function(input, output, session) {
      
      observeEvent(watch("change_name"), {
        
        output$output_name <- renderText(r6$name)
      })
    }
  )
}


# Main app ------------------------------------------------------------------------------


ui <- fluidPage(
  
  mod_1_UI(id = "mod_1"),
  mod_2_UI(id = "mod_2")
)

server <- function(input, output, session) {
  
  hello_r6 <- ExampleR6$new()
  
 init("change_name")
  
  mod_1_Server(id = "mod_1", r6 = hello_r6)
  mod_2_Server(id = "mod_2", r6 = hello_r6)
}

shinyApp(ui, server)

• r
• shiny
• r6

1 Answer 1

There is a lot more going on in your MRE than just using R6. I'm not sure what you're trying with the initialize = part - setting name = "Eric" is sufficient and you can tell that by printing hello_r6$name in the main server. The reason your MRE doesn't work is that you are overwriting the initial value in mod1 with r6$name <- input$input_name . If you wrap that like this it will work as expected:

 if (input$input_name != ""){
   r6$name <- input$input_name
 }

Putting output inside observeEvent is not best practice. This is a better alternative to achieve the same result with {gargoyle}:

output$output_name <- renderText({
                        watch("change_name")
                        r6$name
                       })