Nullable Reference Class Fields

gistfile1.r

nullable = function(name) {
  union_name = paste(name, 'NULL', sep='_')

  tryCatch({
    # existing definition
    getClass(union_name)
    return(union_name)
  },
  error=function(e) {
    # new definition
    return(setClassUnion(union_name , c(name, 'NULL')))
  })
}

X = setRefClass('X',
  fields=list(name=nullable('character')),
  methods=list(
    initialize=function(name=NULL) {
      .self$name = name

      return(.self)
    }
  )
)

x = X$new()
y = Y$new('Josh')