Re: scope of variable in NCL

Hi Dave and Wei and others,

Thanks for the feedback and clarification. I understand it
, but doesn't it illustrate a situation, where some unsuspecting
user accidentally uses the same name somewhere in his script
as the function argument and lands up a nasty surprise. If the
library developer cannot ensure the 'local' scope of the arguments
within the function, it is a bit inconvenient, as the developer
has to be careful not to change the arguments that are passed on
to the function. I still wonder why this behaviour is implemented
in NCL functions, as a function is supposed to return a single data object.
...why should it change other variables or arguments that it does not
return. Also this means that there is no real difference between a
so called 'procedure' and 'function'. If I am a paranoid user, I would have
to check all function definitions, before I feel confident to use them.

I wonder if it will be possible to rethink this design issue in NCL at
least for functions --

Best regards,
saji

* David Brown <dbrown@ucar.edu> [2009-10-16 09:29:30 -0600]:

> Hi Saji,
> Wei is quite correct about this case. Arguments are passed by
> reference and the variables they reference can be modified inside
> the function. The 'local' statement has no meaning for arguments.
> You can ignore the last message I sent. I apologize that I did not
> notice that 'a' was being used as an argument to the function.
> -dave
>
> On Oct 16, 2009, at 8:09 AM, Wei Huang wrote:
>
> >Saji,
> >
> >That is because you use "a" as an argument element, and local.
> >
> >If you do "print("" + test(0,1,2))", then you can not change "a"
> >out side your function.
> >
> >Wei Huang
> >huangwei@ucar.edu
> >VETS/CISL
> >National Center for Atmospheric Research
> >P.O. Box 3000 (1850 Table Mesa Dr.)
> >Boulder, CO 80307-3000 USA
> >(303) 497-8924
> >
> >
> >
> >
> >
> >On Oct 15, 2009, at 11:03 PM, Saji N Hameed wrote:
> >
> >>Even declaring "a" as local does not seem to work :(
> >>ncl 1> function test(a,b,c)
> >>ncl 2> local a,b,c
> >>ncl 3> begin
> >>ncl 4> a=-999
> >>ncl 5> return(1)
> >>ncl 6> end
> >>ncl 7> print(""+test(a,1,2))
> >>(0) 1
> >>ncl 8> print(""+a)
> >>(0) -999
> >>
> >>* Saji N Hameed <saji@apcc21.net> [2009-10-16 13:59:15 +0900]:
> >>
> >>>Dear NCL Developers,
> >>>
> >>>I suppose that the following should not happen. Isn't it a bug?
> >>>We are told that variables inside a function have local scope, and
> >>>this unusual feature can lead to a lot of headaches. Any solutions,
> >>>other than "local a" or using another variable name than "a"
> >>>
> >>>Copyright (C) 1995-2009 - All Rights Reserved
> >>>University Corporation for Atmospheric Research
> >>>NCAR Command Language Version 5.1.1
> >>>The use of this software is governed by a License Agreement.
> >>>See http://www.ncl.ucar.edu/ for more details.
> >>>ncl 0> a=5
> >>>ncl 1> function testme(a,b,c)
> >>>ncl 2> begin
> >>>ncl 3> a=2
> >>>ncl 4> return(1)
> >>>ncl 5> end
> >>>ncl 6> print(""+a)
> >>>(0) 5
> >>>ncl 7> print(""+testme(a,1,2))
> >>>(0) 1
> >>>ncl 8> print(""+a)
> >>>(0) 2
> >>>
> >>>Thanks,
> >>>saji
> >>>--
> >>>
> >>>
> >>>_______________________________________________
> >>>ncl-talk mailing list
> >>>List instructions, subscriber options, unsubscribe:
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> >>>
> >>
> >>-- Saji N. Hameed
> >>
> >>APEC Climate Center
> >>1463 U-dong, Haeundae-gu, +82 51 745
> >>3951
> >>BUSAN 612-020, KOREA saji@apcc21.net
> >>Fax: +82-51-745-3999
> >>
> >>
> >>
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>

-- 
Saji N. Hameed
APEC Climate Center          				
1463 U-dong, Haeundae-gu,                               +82 51 745 3951
BUSAN 612-020, KOREA                    		saji@apcc21.net
Fax: +82-51-745-3999
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