Getting and Setting with Active Bindings

Object-Oriented Programming with S3 and R6 in R

Richie Cotton

Data Evangelist at DataCamp

ch3_3-getting-and-setting-with-active-bindings.003.png

getting = read the data field

setting = write the data field

Active Bindings

defined like functions

accessed like data variables

thing_factory <- R6Class(
  "Thing",
  private = list(
    ..a_field = "a value",
    ..another_field = 123
  ),
  active = list(

    a_field = function() {

      if(is.na(private$..a_field)) {
        return("a missing value")
      }

      private$..a_field

    },

    another_field = function(value) {

      if(missing(value)) {
        private$..another_field
      } else {

        assert_is_a_number(value)

        private$..another_field <- value
      }

    }

  )
)

a_thing <- thing_factory$new()

a_thing$a_field

"a value"

a_thing$a_field <- "a new value"

Error in (function (value)  : a_field is read-only.

a_thing$another_field <- 456

a_thing$another_field <- "456"

Error in (function (value) : is_a_number : 
value is not of class 'numeric'; it has class 'character'.

Summary

Control private access with active bindings
Defined like functions
Accessed like data

Let's practice!

Object-Oriented Programming with S3 and R6 in R