Re: Passing optional parameters through a wrapper routine

[davidf(at)dfanning.com (David Fanning)]

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

> The _EXTRA keyword handles passing keyword parameters through a wrapper
> routine, but what about optional parameters?  

_Extra (and _Ref_Extra, for that matter) apply only to *KEYWORD*
parameters. Positional parameters do not count.

> 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
> ...

That's one way to do it. :-)

Another way is to define any parameter that is NOT passed
in. That might make more sense, since this is standard
operating procedure for any optional parameter.

IF N_Elements(y0) EQ 0 THEN y0 = 0
IF N_Elements(nx) EQ 0 THEN nx = 100
etc.

> (Is TVRD just counting the number of passed
> parameters and not checking to see if they are defined?)

Hard to know what TVRD is doing, but what *you*
better be doing is making sure any variable you
plan to use is defined. :-)

Cheers,

David
-- 
David Fanning, Ph.D.
Fanning Software Consulting
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