[fitsbits] Abuse of EXTEND keyword

[William Pence]

Keep in mind that if a keyword is officially "deprecated", then we are 
telling software developers that they really should change their 
software that creates FITS files so that it no longer writes the keyword 
(unless one claims the loophole that applications that already use a 
deprecated structure can continue to use it).  Simply making the keyword 
optional would have less impact on developers and users.  For example, 
if I were mandated to change CFITSIO to no longer write the EXTEND 
keyword (it currently automatically writes EXTEND = T in every new FITS 
file), then after projects upgrade to the new version, their FITS files 
will suddenly be different than before.  The change should be harmless, 
but still this may cause their regression testing to fail.

arne wrote:
> I don't think you can have it both ways.
> 
> If currently, you can have extensions *without* having
> EXTEND=T in the initial header, then by the "once FITS,
> always FITS" rule, EXTEND=T has no meaning.  To me, it
> originally had value because I didn't have to figure out
> where the next header was (I just returned an error if
> that was attempted without EXTEND=T), but if you've allowed
> other uses, you have to live with it and just create more
> headache for the software developers.
> 
> Deprecate it.  I agree with Arnold and others.
> Arne
-- 
____________________________________________________________________
Dr. William Pence                       pence at milkyway.gsfc.nasa.gov
NASA/GSFC Code 662       HEASARC        +1-301-286-4599 (voice)
Greenbelt MD 20771                      +1-301-286-1684 (fax)