Environments, Reference Behavior, & Shared Fields

Object-Oriented Programming with S3 and R6 in R

Richie Cotton

Data Evangelist at DataCamp

list

environment

env <- new.env()

lst <- list(x = pi ^ (1:5), y = matrix(month.abb, 3))

env$x <- pi ^ (1:5)
env[["y"]] <- matrix(month.abb, 3)

lst

$x
3.141593   9.869604  31.006277  97.409091 306.019685

$y
     [,1]  [,2]  [,3]  [,4] 
[1,] "Jan" "Apr" "Jul" "Oct"
[2,] "Feb" "May" "Aug" "Nov"
[3,] "Mar" "Jun" "Sep" "Dec"

env

<environment: 0x103f3dfc8>

ls.str(lst)

x :  num [1:5] 3.14 9.87 31.01 97.41 306.02
y :  chr [1:3, 1:4] "Jan" "Feb" "Mar" "Apr" "May" ...

ls.str(env)

x :  num [1:5] 3.14 9.87 31.01 97.41 306.02
y :  chr [1:3, 1:4] "Jan" "Feb" "Mar" "Apr" "May" ...

lst2 <- lst
(lst$x <- exp(1:5))

2.718282   7.389056  20.085537  54.598150 148.413159

lst2$x

3.141593   9.869604  31.006277  97.409091 306.019685

identical(lst$x, lst2$x)

FALSE

env2 <- env
(env$x <- exp(1:5))

2.718282   7.389056  20.085537  54.598150 148.413159

env2$x

2.718282   7.389056  20.085537  54.598150 148.413159

identical(env$x, env2$x)

TRUE

copy by value

copy by reference

thing_factory <- R6Class(
  "Thing",
  private = list(

    shared = {

      e <- new.env()

      e$a_shared_field = 123

      e

    }

  ),

  active = list(
    a_shared_field = function(value) {
      if(missing(value)) {
        private$shared$a_shared_field
      } else {
        private$shared$a_shared_field <- value
      }
    }
  )

)

a_thing <- thing_factory$new()
another_thing <- thing_factory$new()

a_thing$a_shared_field

another_thing$a_shared_field

a_thing$a_shared_field <- 456
another_thing$a_shared_field

Summary

Create environments with new.env()
Manipulate them using list syntax
Environments copy by reference
Share R6 fields using an environment field

Let's practice!

Object-Oriented Programming with S3 and R6 in R