How-to: Use destructure operator

Note: The destructure operator is currently an experimental feature and its behavior may change in future releases.

Overview

The destructure operator %<-% allows you to extract multiple named values from a list into individual variables in a single assignment. While it was originally introduced to improve the ergonomics of working with Shiny modules, its clean syntax makes it valuable for any situation where you need to unpack multiple values from a named list.

Basic Usage

The operator works with any named list in R. The basic syntax is:

c(var1, var2) %<-% list_object

Here are the key features:

1. Named List Requirements
   • The right-hand side must be a named list
   • Data frames are not supported
   • Unnamed lists will raise an error
2. Partial Extraction
   • You can extract only the values you need
   • Order doesn’t matter - matching is done by name

# Create a list with named elements
config <- list(host = "localhost", port = 8080, debug = TRUE)

# Extract only what you need
c(host, port) %<-% config

3. Pipe Operator Compatibility
   • Works with the native pipe operator (|>)
   • Requires wrapping the piped expression in parentheses

c(value) %<-% (
  123 |>
    list(value = _)
)

Shiny Modules Integration

The destructure operator particularly shines when working with Shiny modules. Here’s a practical example:

# app/view/module.R

box::use(
  shiny[div, moduleServer, NS, numericInput, reactive],
)

#' @export
ui <- function(id) {
  ns <- NS(id)
  div(
    numericInput(ns("number"), "Enter a number", value = 0),
    numericInput(ns("number2"), "Enter another number", value = 0),
  )
}

#' @export
server <- function(id) {
  moduleServer(id, function(input, output, session) {
    return(list(
      number = reactive(input$number),
      number2 = reactive(input$number2)
    ))
  })
}

# app/main.R

box::use(
  rhino[`%<-%`],
  shiny[div, moduleServer, NS, renderText, textOutput],
)

box::use(
  app/view/module,
)

#' @export
ui <- function(id) {
  ns <- NS(id)
  div(
    module$ui(ns("module")),
    textOutput(ns("result"))
  )
}

#' @export
server <- function(id) {
  moduleServer(id, function(input, output, session) {
    # Clean extraction of multiple reactive values
    c(number, number2) %<-% module$server("module")

    output$result <- renderText({
      paste0("Sum of ", number(), " and ", number2(), " is ", number() + number2())
    })
  })
}

In this example, the module’s server function returns a list of reactive values. The destructure operator provides a clean and intuitive way to extract these values into separate variables, making the code more readable and maintainable.