Non-standard set-functions in R Reference Classes

Question

Is it possible to get the syntax

foo$bar(x) <- value

to work where foo is a reference class object and bar is a method? I.e. is it possible to do "subset assigment" and have "replacement functions" as methods in Reference Classes?

Is the syntax possible to get with other OO systems?

Example: I'll illustrate with a made-up use case. Imagine a reference class, Person, which contains some basic information of a person. Particularly, one field called fullname is a named list:

PersonRCGen <- setRefClass("Person",
                           fields = list(
                             fullname = "list",
                             gender = "character"
                           ))

Next, we should define some methods to get and set particular names within the fullnames list which (try) to give the above syntax/interface. My best attempt has so far been:

PersonRCGen$methods(
  name = function(x) { # x is the dataset,
    .self$fullname[[x]]
  },
  `name<-` = function(x, value) {
    .self$fullname[[x]] <- value
  }
)

The naming here should also illustrate what I'm trying to do.

We initialize a new object:

a_person <- PersonRCGen$new(fullname = list(first = "Jane", last = "Doe"),
                            gender = "F")

Accessing the fullname field directly and accessing the first and last name by the defined get-function works as intended:

a_person$fullname
#$`first`
#[1] "Jane"
# 
#$last
#[1] "Doe"

a_person$name("first")
#[1] "Jane"

a_person$name("last")
#[1] "Doe"

However, for setting a particular name in the fullname list, I'd like to have the following syntax/interface which unfortuantely fails.

a_person$name("first") <- "Jessie"
#Error in a_person$name("first") <- "Jessie" : 
#  target of assignment expands to non-language object

I know the following works (which basically renders the method poorly named).

a_person$`name<-`("first", "Johnny")
a_person$fullname
#$`first`
#[1] "Johnny"
#
#$last
#[1] "Doe"

In my real use case, I'd like to avoid 'traditional' getName(x) and setName(x, value) names for the get and set functions.

Answer 1

I don't think you can do this with your desired syntax.

Note that you will get the same error if you run any assignment like that, e.g.

a_person$hello("first") <- "John"

so it's really a basic problem.

What does work, is the following syntax:

name(a_person, "first") <- "John"

Altogether you could then have something like below:

PersonRCGen <- setRefClass("Person",
                  fields = list(
                    fullname = "list",
                    gender = "character"
                  ),
                  methods = list(
                    initialize = function(...) {
                      initFields(...)
                    },
                    name = function(x) {
                      .self$fullname[[x]]
                    }
                  )
)

setGeneric("name<-", function(x, y, value) standardGeneric("name<-"))
setMethod("name<-", sig = "ANY", function(x, y, value) {
  UseMethod("name<-")
})
# some extras
"name<-.default" <- function(x, y, value) {
  stop(paste("name assignment (name<-) method not defined for class", class(x)))
}
"name<-.list" <- function(x, y, value) {
  x[[y]] <- value
  return(x)
}
# and here specifically
"name<-.Person" <- function(x, y, value) {
  x$fullname[[y]] <- value
  return(x)
}

# example to make use of the above
a_person <- PersonRCGen$new(
  fullname = list(
    first = "Jane",
    last = "Doe"
  ),
  gender = "F"
)

a_person$name("first")
#> [1] "Jane"
name(a_person, "middle") <- "X."
a_person$name("middle")
#> [1] "X."

I'm aware this is not exactly what you want but I hope it helps.

Answer 2

I am probably misunderstanding what you are trying to achieve but what's wrong with this?

person = setRefClass("Person",
                     fields = list(
                       fullname = "list",
                       gender = "character"
                     ))

a_person = person$new(fullname = list(first = "James", last = "Brown"), gender="M")

a_person$fullname$first = "Bob"

a_person

Reference class object of class "Person"
Field "fullname":
$`first`
[1] "Bob"

$last
[1] "Brown"

Field "gender":
[1] "M"