Re: Top 10 IDL Requests

[Craig Markwardt <craigmnet(at)cow.physics.wisc.edu>]

davidf@dfanning.com (David Fanning) writes:

> Craig Markwardt (craigmnet@cow.physics.wisc.edu) writes:
> 
> > davidf@dfanning.com (David Fanning) writes:
> > > Vinay L. Kashyap (kashyap@head-cfa.harvard.edu) writes:
> > > > 2. _EXTRA
> > > > 
> > > > Please consider having all built-in commands accept _EXTRA as a keyword.
> > > 
> > > Uh, this is the way it works. :-)
> > 
> > Uh, not quite.  There are some built in commands that don't accept any
> > keywords at all.  The _EXTRA keyword doesn't work for them, *even* if
> > the value passed is empty!
> > 
> > Why is this important?  Makes it a pain to write a wrapper procedure
> > or function.
> 
> Alright, I must be obtuse today, but I can't figure out why
> it would be hard to write wrapper routines for commands that
> don't take keywords. Surely in writing the wrapper you give
> at least *some* thought to what keywords you might expect
> to be passed. Adding an _Extra to such a command seems
> excessively anal at the very least, and certainly unnecessary. :-)
> 
> And what commands did you have in mind? I've never encountered
> a built-in command that didn't accept this keyword mechanism.

Hrmm.  The moment I need to find an example, and I can't find it.
Arghh.  An example of a built-in command that doesn't take keywords is
EMPTY, but I agree that it's a pretty lame example.  I actually would
hope that *all* procedures and functions could be called with _EXTRA,
whether or not they actually accept keywords.  For, example, this
statement

  call_procedure, 'EMPTY', _EXTRA=null

will fail no matter what, even if null is an undefined variable.
Shouldn't IDL be smart enough to test whether the _EXTRA value is
undefined before it crashes?

I'm always looking for ways to avoid special cases in wrapper
routines.  Real world examples of such unavoidable abominations are
given below.

Craig


(from XFWINDOW in XFWINDOW_CALL_PROCEDURE)
  sz = size(key)   
  if sz(sz(0)+1) EQ 8 then begin ;; Keywords are present
      xfwindow_rekey, key
      case n_args of 
          0: call_procedure, cmd, _extra=key
          1: call_procedure, cmd, x0, _extra=key
          2: call_procedure, cmd, x0, x1, _extra=key
          3: call_procedure, cmd, x0, x1, x2, _extra=key
          4: call_procedure, cmd, x0, x1, x2, x3, _extra=key
          5: call_procedure, cmd, x0, x1, x2, x3, x4, _extra=key
      endcase
  endif else begin               ;; No keywords are present
      case n_args of 
          0: call_procedure, cmd
          1: call_procedure, cmd, x0
          2: call_procedure, cmd, x0, x1
          3: call_procedure, cmd, x0, x1, x2
          4: call_procedure, cmd, x0, x1, x2, x3
          5: call_procedure, cmd, x0, x1, x2, x3, x4
      endcase
  endelse

(from MPFIT in MPFIT_CALL)
  if proc then begin
      if n_params() EQ 3 then begin
          if n_elements(extra) GT 0 then $
            call_procedure, fcn, x, f, fjac, _EXTRA=extra $
          else $
            call_procedure, fcn, x, f, fjac
      endif else begin
          if n_elements(extra) GT 0 then $
            call_procedure, fcn, x, f, _EXTRA=extra $
          else $
            call_procedure, fcn, x, f
      endelse
  endif else begin
      if n_params() EQ 3 then begin
          if n_elements(extra) GT 0 then $
            f = call_function(fcn, x, fjac, _EXTRA=extra) $
          else $
            f = call_function(fcn, x, fjac)
      endif else begin
          if n_elements(extra) GT 0 then $
            f = call_function(fcn, x, _EXTRA=extra) $
          else $
            f = call_function(fcn, x)
      endelse
  endelse  

-- 
--------------------------------------------------------------------------
Craig B. Markwardt, Ph.D.         EMAIL:    craigmnet@cow.physics.wisc.edu
Astrophysics, IDL, Finance, Derivatives | Remove "net" for better response
--------------------------------------------------------------------------