DEFSTATIC

(defstatic var-name [initial-value-expression])

(defstatic cache (array))   ; create a cached array
(defstatic count 0)         ; initialise a function counter

This instruction asks that the named variable be of a type that maintains its state across invocations of a file unit or function call. **An optional initial value* may be supplied. If not initial value is given then the default behaviour is unspecified by FELT; it is the behaviour of the chosen target back-end language that will dictate what happens at execution time.

---

Local static variables

Some but not all languages allow the concept of "static" variables such that within a particular scope, be it file or functional, that variable maintains whatever state state it has across invocations of a function.

This allows functions to be able to implement simple cache or memoization behaviours as the "static" variable does not get re-set each time the function is called.

Classic PHP Usage

The following FELT code shows how you might use DEFSTATIC variable within the scope of a function to maintain a list of results: this is a very simple memoization scheme and, at the expense of memory it will provide faster response times:

(defun do-query(query-string)
  (defstatic cache [])
  (defvar hash (md5 query-string))
  (if (isset (@ cache hash))
      (return (@ cache hash)))
  ;; first time here, do it...
  (= (@ cache hash)
     (execute-query query-string))
  (return (@ cache hash)))

The rendered PHP code for the above example is:

function do_query($query_string) {
  static $cache = array();
  $hash = md5($query_string);
  if (isset($cache[$hash])) {
    return $cache[$hash];
  }
  $cache[$hash] = execute_query($query_string);
  return $cache[$hash];
}

JavaScript does not have this feature and just defines a normal locally scoped variable instead.

function do_query($query_string) {
  static $cache = array();
  $hash = md5($query_string);
  if (isset($cache[$hash])) {
    return $cache[$hash];
  }
  $cache[$hash] = execute_query($query_string);
  return $cache[$hash];
}