10.7 Fundamentals - Stateful functions

Because

• The enclosing environment is unique and constant, and
• We have <<- (super assignment)

We can change that enclosing environment and keep track of that state across iterations (!)

• <- Assignment in current environment
• <<- Assignment in parent environment

new_counter <- function() {
  i <- 0        
  function() {
    i <<- i + 1 # second assignment (super assignment)
    i
  }
}

counter_one <- new_counter()
counter_two <- new_counter()
c(counter_one(), counter_one(), counter_one())
#> [1] 1 2 3
c(counter_two(), counter_two(), counter_two())
#> [1] 1 2 3

“As soon as your function starts managing the state of multiple variables, it’s better to switch to R6”