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Re: IDL 8.0 compile_opt changes [message #69328 is a reply to message #69187] Wed, 06 January 2010 06:56 Go to previous messageGo to previous message
Yngvar Larsen is currently offline  Yngvar Larsen
Messages: 134
Registered: January 2010
Senior Member
My 2 cents:

*) About negative indexing:

> For example:
>
> a[0:-1] In IDL80, returns all the elements
> a[-1] In IDL80, returns the last element

Is the only use for negative indexing a way to indicate the last
element? Then this is probably the most idiotic choice possible:
semantic overload of the integer -1 with no gain whatsoever (except
possibly in ITTVis' parsing code that might be simplified by some
clever tricks?). Why not use some other syntactic element like the
string 'end' (like matlab) or 'last' or '%' or whatever?

Or is there some other clever use? Reverse/step indexing like matlab's
"array(first:step:last)" with negative steps allowed would be
fantastic, but this doesn't require negative indices at all. I
propose:
IDL8> array = indgen(5)
IDL8> print, array[%:1:-2] ; array[first:last:step] like the FOR loop
indexing
4 2
IDL8> print, array[%]
4
IDL8> print, array[%/2]
2

etc

*) about '.' instead of '->':

NO,NO,NO!

IDL is not Python, as some people have pointed out. Any syntax that
requires access to the dynamic runtime to be resolved is a Bad Idea,
which is why the transition from () to [] was a Good Idea. I agree
that '.' looks better than '->', but unless access to the internal
'self' structure is allowed from outside of objects, like in Python, I
see absolutely no point in looking superficially like Python. That
would in fact be _more_ confusing since it is not the same. Semantics
is more important than syntax at the end of the day.

*) about legacy libraries:

> 2. Do you use existing libraries (like Astrolib or JHUAPL's) that
> would break? Could ITTVIS retrofit these 2 libraries and give them
> back to the community?

That would be the best solution to avoid scaring the many(?) users of
these libraries from upgrading. And how about a tool in the IDE to
convert legacy code from old to new style, i.e. () to [] and -> to '.'
if this is chosen, optionally interactively. Also maybe including
indicating common pitfalls like formatted IO for manual inspection.
Should be easy to get 99% right as many already commented on.

*) about default 'idl2' breaking code:

In my opinion, code that is broken by this (mostly formatted IO for
binary files of a specific format without specifying explicit
datatypes) is in fact already broken by design. Or at least badly
written.

I vote for default 'idl2'. 13 years of transition should be
sufficient...

*) about a new extension for >=8.0 code: I hate the idea, though it
solves the problem. I like better the idea of using the comment
character e.g. ;%compile_opt idl1. It is butt ugly, but so is the code
that needs it :)

*) about other issues for 8.0 (according to
http://michaelgalloy.com/2009/12/28/agu-idl-users-group-meet ing.html#more-2092):

- operator overloading: nice!!
- null elements for arrays and structures: nice!! ('[]' and '{}'?)
- FOREACH loop: very useful. Even better if new data types like maps/
lists/hashtables are planned.

Wishlist:
- More general datatypes like map/list/hashtable/tuple etc.
- I wish a scalar and an array with one element could be treated as
different datatypes. Mathematically, they are different, so sometimes
confusing bugs are caused by conflating them like IDL currently does.
- object based widgets anyone? And when will the new widgets used for
the Workbench be available for users? Motif looks so last millenium...
- some kind of package system or namespaces to avoid having to call my
own library functions/procedures/objects something like
" reallylongstringtominimizeprobabilityfornameclashes_myfuncti on "

--
Yngvar

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