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Exercise

First Thing's First

There is one special public method named initialize() (note the American English spelling). This is not called directly by the user. Instead, it is called automatically when an object is created; that is, when the user calls new().

initialize() lets you set the values of the private fields when you create an R6 object. The pattern for an initialize() function is as follows:

thing_factory <- R6Class(
  "Thing",
  private = list(
    a_field = "a value",
    another_field = 123
  ),
  public = list(
    initialize = function(a_field, another_field) {
      if(!missing(a_field)) {
        private$a_field <- a_field
      }
      if(!missing(another_field)) {
        private$another_field <- another_field
      }
    }
  )
)

Notice the use of missing() (docs). This returns TRUE if an argument wasn't passed in the function call.

Arguments to the factory's new() method are passed to initialize().

a_thing <- thing_factory$new(
  a_field = "a different value", 
  another_field = 456
)

Instructions

100 XP

A microwave oven factory has been partially defined for you.

  • Add a public method named initialize(). This should allow the user to set the power_rating_watts and door_is_open fields when the object is created.
    • The arguments should be power_rating_watts and door_is_open.
    • In the body of the initialize() method, for each argument, if it is not missing() (docs), then the corresponding private field should be set.
  • Create a microwave object with a power rating of 650 watts, and an open door.
    • Call microwave_oven_factory's new() method.
    • Pass the arguments power_rating_watts = 650 and door_is_open = TRUE to new().
    • Assign the result to a_microwave_oven.