state

The goal of state is to provide an alternative to shiny::reactiveValues() that includes type safety functionality. Create a type safe reactiveValues with state_manager() and initialize values with state(), where the first argument is the initial value and the second one is the expected S7 class.

Installation

You can install the development version of state like so:

pak::pak("calderonsamuel/state")

Example

This is a basic example which shows you how to solve a common problem:

library(state)

Create a state manager

sm <- state_manager()

Initialize some state

sm$counter <- state(0L, S7::class_integer)

It will error if you try to assign a different type

sm$counter <- "new value"
#> Error: Invalid type for 'counter': expected <integer>, got <character>.

Or if you try to initialize state without using state()

sm$new <- 0L
#> Error: No type defined for 'new'. Assign a <state> object first.

It will work if you assign a value of the expected class

sm$counter <- 1L

You can use it as a typical reactiveValues object

shiny::isolate(sm$counter)
#> [1] 1

You can also use key S3 classes provided by the base packages

sm$df <- state(mtcars, S7::class_data.frame)
sm$date <- state(as.Date("2025-01-01"), S7::class_Date)

Or provide your custom S7 classes

animal <- S7::new_class(
  name = "animal",
  properties = list(
    n_legs = S7::class_integer
  )
)

bird <- animal(n_legs = 2L)
dog <- animal(n_legs = 4L)

sm$my_animal <- state(bird, animal)
sm$my_animal <- dog
shiny::isolate(sm$my_animal)
#> <animal>
#>  @ n_legs: int 4