S3 Enums

S3enum.R

enum <- function(...) {
  vals <- if (is.null(...names())) {
    setNames(seq_len(...length()), c(...))
  } else {
    c(...)
  }
  out <- new.env(parent = emptyenv())
  list2env(as.list(vals), out)
  lapply(names(vals), lockBinding, out)
  lockEnvironment(out)
  class(out) <- "enum"
  out
}

print.enum <- function(x, ...) {
  cat("An enum with", length(x)  ,"levels:\n")
  print(ls(x))
}

dirs <- enum("north", "east", "south", "west")
dirs
#> An enum with 4 levels:
#> [1] "east"  "north" "south" "west"
dirs$north
#> [1] 1

dirs$down <- 5
#> Error in dirs$down <- 5: cannot add bindings to a locked environment
dirs$north <- 7
#> Error in dirs$north <- 7: cannot change value of locked binding for 'north'

"north" %in% names(dirs)
#> [1] TRUE

dirs <- enum("north" = 3, "east" = 4, "south" = 5, "west" = 6)
dirs
#> An enum with 4 levels:
#> [1] "east"  "north" "south" "west"
dirs$north
#> [1] 3