14.17 Adding a read-only bank account number

BankAccount <- R6Class("BankAccount", public = list(
  owner = NULL,
  type = NULL,
  balance = 0,
  initialize = function(owner, type, acct_num = NULL) {
    private$acct_num <- acct_num
    self$owner <- owner
    self$type <- type
  },
  deposit = function(amount) {
    self$balance <- self$balance + amount
    invisible(self)
  },
  withdraw = function(amount) {
    self$balance <- self$balance - amount
    invisible(self)
  },
  print = function(...) {
    cat("Account owner: ", self$owner, "\n", sep = "")
    cat("Account type: ", self$type, "\n", sep = "")
    cat("Account #: ", private$acct_num, "\n", sep = "")
    cat("  Balance: ", self$balance, "\n", sep = "")
    invisible(self)
  }
  ),
  private = list(
    acct_num = NULL
  ),
  active = list(
    create_acct_num = function(value) {
      if (is.null(private$acct_num)) {
        private$acct_num <- ids::uuid()
      } else {
        stop("`$acct_num` already assigned")
      }
    }
  )
)

collinsavings <- BankAccount$new("Collin", type = "Savings")
collinsavings$create_acct_num
# Stops because account number is assigned
collinsavings$create_acct_num()
collinsavings$print()