Four Js Development Tools Forum

Here I go again with NULL...

I recently found a bug in our code where where are checking if a passed in parameter (happens to be a DICTIONARY) to a function is null.  Turns out the dictionary can never be null.  This is very odd -- is that the indented behavior? I guess this is similar behavior to ARRAY?

MAIN
 
  CALL check_dictionary(NULL)
 
END MAIN
 
FUNCTION check_dictionary(dict)
 
  DEFINE dict DICTIONARY OF STRING
 
  DISPLAY "Passed in Dictionary"
  IF dict IS NULL THEN
    DISPLAY "dict IS NULL"
  ELSE
    DISPLAY "dict IS NOT NULL"
  END IF
 
  DISPLAY ""
  DISPLAY "LET dict = NULL"
  LET dict = NULL
  IF dict IS NULL THEN
    DISPLAY "dict IS NULL"
  ELSE
    DISPLAY "dict IS NOT NULL"
  END IF
 
  DISPLAY ""
  DISPLAY "INITIALIZE dict to NULL"
  INITIALIZE dict TO NULL
  IF dict IS NULL THEN
    DISPLAY "dict IS NULL"
  ELSE
    DISPLAY "dict IS NOT NULL"
  END IF
 
END FUNCTION
 

Output:
Passed in Dictionary
dict IS NOT NULL

LET dict = NULL
dict IS NOT NULL

INITIALIZE dict to NULL
dict IS NOT NULL

According to the documentation the DICTIONARY array is passed to/from functions by reference on the stack and not by value. Use the getLength() method to check if the dictionary is empty.


On the subject of DICTIONARY it would be nice to have the option to sort them into key order...

I am surprised that "IF dict IS NULL" compiles.  I would expect similar to  "IF arr IS NULL" which generate a -4340 error, and that the correct test would be  "IF dict.getLength() = 0" just like dynamic array case "IF arr.getlength() = 0".


Just sort the keys array.

LET keys = dict.getkeys()
CALL keys.sort(NULL, FALSE)

Hello,

In upcoming FGL versions 3.10.18 and FGL 3.20.04 (this is not in 3.20 EAP3!), the compiler will raise the error -4340 when using a dictionary in expressions like IF dict IS NULL THEN:

MAIN
    DEFINE dict DICTIONARY OF STRING
    IF dict IS NULL THEN
| The variable 'dict' is too complex a type to be used in an expression.
| See error number -4340.
        DISPLAY "dict IS NULL"
    ELSE
        DISPLAY "dict IS NOT NULL"
    END IF
END MAIN

Seb

Good point, I forgot about that one! Thanks.