Object-Oriented Programming

Objects as closures#

It can be succinct to implement an object using closures. Here is an excellent example from Ross and Robert (1996), p.304:

#! config(debug = T, deparsers = default_2_deparsers())
account <- function(total) {
    list(balance = function() total,
         deposit = function(amount) total <<- total + amount,
         withdraw = function(amount) total <<- total - amount)
}

Robert <- account(1000)
Ross <- account(500)

Robert$deposit(100)
Ross$withdraw(150)

print(Robert$balance())  # expect 1100
print(Ross$balance())    # expect 350

R6 style of declaration#

The sketch package supports object declaration using the R6 OOP syntax. Here is an example:

reactive <- R6Class(
    "reactive", 
    public = list(
        value_1 = NULL,
        method_1 = function() {
            print("Method 1 called")
            print("    value_1: " %+% self$value_1)
            print("    value_2: " %+% private$value_2)
        },
        initialize = function(x, y) {
            self$value_1 <- x
            private$value_2 <- y
            return(self)
        }
    ), 
    private = list(
        value_2 = NULL
    )
)

# Usage
x <- reactive$new(1, 999)
print("Fields and methods available to users: " %+% names(x))
x$method_1()