[R] Enumeration in R

[Paul Roebuck]

I want the equivalent of this 'C' declaration.
    enum StoplightColor {
        green = 3,
        yellow = 5,
        red = 7
    };

This mostly works except the validity checking doesn't
seem to occur automatically. What didn't I do to enable
it?

setClass("stoplightColor",
         representation(value = "integer"),
         prototype = integer(1))
stoplightColor <- function(value) {
    if (missing(value))
        stop('no value!')
    new("stoplightColor", value)
}
valid.stoplightColor <- function(object) {
    valid <- switch(as(object at value, "character"),
                    "3" = TRUE,
                    "5" = TRUE,
                    "7" = TRUE,
                    FALSE)
    if (valid == FALSE)
        return("Value not in list of valid values [3|5|7]");
    return(TRUE);
}
setValidity("stoplightColor", valid.stoplightColor)
initialize.stoplightColor <- function(.Object, value) {
    .Object at value <- as.integer(value)
    .Object
}
setMethod("initialize",
          signature(.Object = "stoplightColor"),
          initialize.stoplightColor)
green <- stoplightColor(3)
yellow <- stoplightColor(5)
red <- stoplightColor(7)

# error: no value argument
noarg <- stoplightColor()

# error: invalid number argument
bad <- stoplightColor(6)      # WHY NO WARNING HERE?
validObject(bad)


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SIGSIG -- signature too long (core dumped)