Re: Named Indices

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

J.D. Smith (jdsmith@astro.cornell.edu) writes:

> A slightly more portable solution, in the sense that it requires no modification
> of startup code but simply inclusion of a program somewhere on the path
> (presumably in the same directory tree as the program which would use it), is a
> special purpose function.  E.g.
> 
> plot, findgen(11), LINESTYLE=linestyle(/DASH)
> 
> You could even make an uber-function that encapsulates all such "named
> entity"<->"integer value" constant mappings:
> 
> const(/LINESTYLE,/DASH)  ; produces 2
> 
> const(/AXIS_STYLE,/FORCE,/SUPPRESS) ; produces 4 or 2 = 6
> 
> const(/SIZE,/INTEGER)               ; produces 2
> 
> const(/WIDGET_DRAW_TYPE,/BUTTON_RELEASE) ; produces 1
> 
> const(/AXIS_NUMBER,/X) ; produces 0
> 
> const(/COLOR_TABLE,/PRISM) ; produces 6
> 
> etc.
> 
> The problem is you have to maintain it with new versions of IDL, and ensure
> backwards compatibility too.  Other issues crop up, such as private color table
> lists, etc.  It would definitely help readability though.  Sounds like a great
> beginner programming project that would readily educate one on the subtle
> distinctions among keyword_set(), n_elements() ne 0, and arg_present().  

I thought about a function too, although not such 
a generic one. But I got this far:

   FUNCTION LS, Solid=Solid, Dot=Dot, Dash=Dash, DashDot=DashDot...

When I realized I was in trouble with keyword names.
In the end, I decided cryptic numbers were better
than a long-winded explanation of how keyword names
work. :-(

But what I'm really surprised you didn't offer was
a way to write a polymorphic object to do the job. :-)

Cheers,

David
-- 
David Fanning, Ph.D.
Fanning Software Consulting
Phone: 970-221-0438 E-Mail: davidf@dfanning.com
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