Re: Passing optional parameters through a wrapper routine

[edward.s.meinel(at)aero.org]

In article <950129121.690143@clam-55>,
  "Mark Hadfield" <m.hadfield@niwa.cri.nz> wrote:

> That's an interesting point David. The first few lines
> of my routines tend to look something like this:
>
>  if n_elements(arg1) then message, 'You haven't defined arg1'

...

> 2. The principle that in scientific programming
> (as opposed, say, to Web page programming)
> it is much better for programs to crash than to continue
> and return bad data.

Ugh, I *hate* MESSAGE. Why cause a crash when it is easy to exit nicely?
How about:

  IF N_ELEMENTS(arg1) EQ 0 THEN BEGIN
       print, 'You haven't defined arg1'
       RETURN
  ENDIF

or even:

  IF N_ELEMENTS(arg1) EQ 0 THEN BEGIN
       dummy = DIALOG_MESSAGE('You haven't defined arg1')
       RETURN
  ENDIF

This way the user gets the message, but the program doesn't crash. This
is especially helpful when the procedure is used in a widget -- I don't
have to manually clean up everything before trying again.

>  if size(arg2, /TNAME) ne 'STRING' then message, 'Arg2 must be string
> specifying the file name'

...

> if in doubt, stop and call for help.

Right, but you can stop and ask for help without forcing a crash. How
about:

IF SIZE(arg2, /TNAME) NE 'STRING' THEN BEGIN

; Oooops! forgot the file name.

  arg2 = DIALOG_PICKFILE(set_the_appropriate_keywords)
  IF arg2 EQ '' THEN BEGIN
    dummy = DIALOG_MESSAGE( $
            'You must provide a file name as the second argument')
    RETURN
  ENDIF
ENDIF

Ed Meinel


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