Re: Passing optional parameters through a wrapper routine

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

bowman@null.edu (Kenneth P. Bowman) writes:

> The _EXTRA keyword handles passing keyword parameters through a wrapper
> routine, but what about optional parameters?  If my wrapper for TVRD has
> one of my own (mandatory) parameters, do I have to do the following?
> 
> PRO TVRD_WRAPPER, my_arg, x0, y0, nx, ny, channel, _EXTRA = tvrd_keywords
> 
> CASE N_PARAMS() OF
>    1 : image = TVRD(                         _EXTRA = tvrd_keywords)
>    2 : image = TVRD(x0,                      _EXTRA = tvrd_keywords)
>    3 : image = TVRD(x0, y0,                  _EXTRA = tvrd_keywords)
>    4 : image = TVRD(x0, y0, nx,              _EXTRA = tvrd_keywords)
>    5 : image = TVRD(x0, y0, nx,              _EXTRA = tvrd_keywords)
>    6 : image = TVRD(x0, y0, nx, ny, channel, _EXTRA = tvrd_keywords)
>    ELSE : MESSAGE, 'Incorrect number of arguments.'
> ENDCASE

I have a wrapper procedure in XFWINDOW.PRO which looks remarkably
similar to this one.  To counter David, I find that it's usually the
cleanest and safest bet to mess with as *few* parameters and keywords
as possible when wrapping another function.  You can get into too much
trouble trying to second-guess what the defaults should be.

The ugliness above could be solved if there would be a
variable-parameter feature to the language.  This might work the same
way that _EXTRA passes keywords through.  For example, in

PRO TVRD_WRAPPER, my_arg, $EXTRA_ARGS$, _EXTRA = tvrd_keywords
  image = TVRD($EXTRA_ARGS$,            _EXTRA = tvrd_keywords)
end

the black box variable $EXTRA_ARGS$ would somehow contain any
additional arguments, and could be passed directly through to the
wrapped function.  The use of $'s is syntactic sugar to be sure, but
it's just an example.

Craig

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Craig B. Markwardt, Ph.D.         EMAIL:    craigmnet@cow.physics.wisc.edu
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