R/stack.R

In nick-ulle/rstatic: Low-level Static Analysis Tools for R Code

Stack = R6::R6Class("Stack",
  private = list(
    buffer = NULL,
    len = 0,
    size = 0
  ),

  public = list(
    initialize = function(size = 16, type = "list") {
      private$size = size
      private$buffer = vector(type, private$size)
    },

    peek = function() {
      if (private$len == 0)
        stop("Cannot peek at an empty Stack.")

      return (private$buffer[[private$len]])
    },

    pop = function() {
      if (private$len == 0)
        stop("Cannot pop an empty Stack.")

      x = private$buffer[[private$len]]
      private$buffer[[private$len]] = NA
      private$len = private$len - 1
      return (x)
    },

    push = function(x) {
      if (private$len == private$size) {
        private$size = 2 * private$size
        length(private$buffer) = private$size
      }

      private$len = private$len + 1
      private$buffer[[private$len]] = x
      return (self)
    },

    push_many = function(x) {
      if (length(x) == 0)
        return (self)

      old_len = private$len
      len = old_len + length(x)
      if (len > private$size) {
        private$size = 2 ^ ceiling(log2(len))
        length(private$buffer) = private$size
      }
      
      private$len = len
      private$buffer[(old_len + 1):len] = x
      return (self)
    }
  ),

  active = list(
    is_empty = function() {
      private$len == 0
    }
  )
)