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Re: Generating keyword parameters from strings [message #67404 is a reply to message #67403]

Mon, 27 July 2009 07:39

Paul Van Delst[1]
Messages: 1157
Registered: April 2002

Senior Member

David Fanning wrote:
> Paul van Delst writes:
>
>> Of course it would be nicer if I didn't have to remember it at all. Passing
>> arguments/keywords by reference or value is an implementation detail the user shouldn't be
>> concerned with. Having to consider it in IDL OO programming is mildly ironic.
>
> I think you are forgetting the 80-year history
> of IDL. (Or is it 100? I can never remember.)

Oh no, I'm not forgetting. FORTRAN (which necessarily has a longer history than IDL) had
the same issue although it was a tacit understanding about passing mechanism. I assume IDL
has that restriction because FORTRAN did (IIRC, wasn't IDL orginally written in f77 [or
f66?] on a VMS system? But you would know more about that than me.).

Now that we have Fortran (not all caps, f90 and later) the passing mechanism can vary
based on situation - the compiler can choose the better method (for a suitable definition
of "better").

If you write f90+ code that depends on a particular passing mechanism it's not illegal (in
many cases at least), but you're asking for chunks to be removed from your read-end in the
future. It can suck for some MPI/F90+ amalgams since the former relies on passing by
reference whereas the latter does not.

So, Fortran grew out of the de-facto need to be particular about passing mechanism. I see
no reason why IDL can't. It certainly would make it easier for new users who wonder what
they've done wrong until they discover you can't pass arguments *out* from
procedures/functions when the actual arguments in the calling routine are array elements
or structure components.

cheers,

paulv

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[Message index]

		Re: Generating keyword parameters from strings By: Kenneth P. Bowman on Mon, 27 July 2009 14:26
		Re: Generating keyword parameters from strings By: David Fanning on Mon, 27 July 2009 07:54
		Re: Generating keyword parameters from strings By: Paul Van Delst[1] on Mon, 27 July 2009 07:39
		Re: Generating keyword parameters from strings By: David Fanning on Thu, 23 July 2009 13:03
		Re: Generating keyword parameters from strings By: Paul Van Delst[1] on Thu, 23 July 2009 12:48
		Re: Generating keyword parameters from strings By: Jeremy Bailin on Thu, 23 July 2009 05:14
		Re: Generating keyword parameters from strings By: Giorgio on Wed, 22 July 2009 17:01
		Re: Generating keyword parameters from strings By: Michael Galloy on Wed, 22 July 2009 15:55
		Re: Generating keyword parameters from strings By: Eric Hudson on Wed, 22 July 2009 13:46
		Re: Generating keyword parameters from strings By: David Fanning on Wed, 22 July 2009 11:03
		Re: Generating keyword parameters from strings By: Paul Van Delst[1] on Wed, 22 July 2009 11:00
		Re: Generating keyword parameters from strings By: JDS on Thu, 30 July 2009 08:21

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