Without a constructor

# No constructor: a list tagged with a class
nokia_phone <- structure(list(model = ""),
                         class = "Phone")
nokia_phone$model <- "Nokia 6610"

iphone18 <- structure(list(model = ""),
                      class = "Phone")
iphone18$model <- "iPhone 18"

# No phone yet
kim <- structure(list(first_name = "",
                      last_name = "",
                      personal_phone = NULL),
                 class = "Employee")
# Not assigned yet
no_phone <- is.null(kim$personal_phone)
# no_phone = TRUE

kim$first_name <- "Victoria"
kim$last_name <- "Kim"
kim$personal_phone <- iphone18

cat("no_phone =", no_phone, "\n")
cat("kim$personal_phone$model =",
    kim$personal_phone$model, "\n")
cat("nokia_phone$model =",
    nokia_phone$model, "\n")
cat("class(kim) =", class(kim), "\n")