| Re: Yet again, The Sky is Falling! [message #52967 is a reply to message #52872] |
Fri, 09 March 2007 11:13   |
Michael Galloy
Messages: 1114
Registered: April 2006
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Senior Member |
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On Mar 9, 11:36 am, David Fanning <n...@dfanning.com> wrote:
> Paul van Delst writes:
>> But, then it's not an input parameter. It's an output.
>
> It generally has to get into the program somehow. :-)
>
>> I'm f95-centric, and I know it doesn't apply completely to IDL for a number of reasons,
>> but I don't think people should new code where the functionality depends on *how* the
>> arguments are passed (i.e. by value or reference).
>
> I'm not saying "pass by reference" is not dangerous, it is,
> but it is no more dangerous, it seems to me, than a dynamically
> (and weakly) typed language. Goodness, one of the reasons I LIKE
> IDL is because you can do all these weird things that would
> get your knickers in a snit in some other language.
>
> Sure, you have to learn a few rules, and usually you learn
> them the hard way, but you only have to learn them three or
> four times before they get cemented in your brain. I think
> it is a small price to pay for a LOT of power.
I agree that pass by reference can be dangerous and very useful. To
clarify my "moral":
1. Document clearly which parameters are input, which are output, and
which are both (i.e. modifying a variable "in place"). Don't change
the input ones! If you need to have a default value for that input in
the routine, create a new local variable.
2. Don't pass the same named variable as both an input and output
parameter in a routine call. (Or as two output parameters!)
Mike
--
www.michaelgalloy.com
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