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Re: temporary() problem [message #86026 is a reply to message #86025]

Tue, 24 September 2013 14:29

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

Senior Member

On 09/24/13 16:32, David Fanning wrote:
> spluque@gmail.com writes:
>
>> I'm not sure I understand why the variable 'a' below gets undefined after calling a procedure using temporary():
>>
>> IDL> a='a, b, c'
>> IDL> help, a
>> A STRING = 'a, b, c'
>> IDL> .run "test.pro"
>> % Compiled module: TEST.
>> IDL> test, a
>> IDL> help, a
>> A UNDEFINED = <Undefined>
>>
>>
>> The contents of test.pro:
>>
>> PRO TEST, str
>> ostr=strsplit(temporary(str), ', ', /extract)
>> END
>>
>>
>> Why is temporary() messing with the top level environment?
>
> Because variables are passed by reference in IDL, not by value (copied
> into the procedure). In this case, you are working with the variable str
> itself, not a copy of the variable.

I would go with the explanation that temporary() is "messing" with the
top level environment because that's what the programmer wrote it to do.

"Why is the computer doing what I told it to do, not what I want it to do?"

:o)

For the OP, try this for some obfuscatory fun:

IDL> a=['qwerty','a,b,c']
IDL> help, a
A STRING = Array[2]
IDL> print, a
qwerty a,b,c
IDL> .run "test.pro"
% Compiled module: TEST.
IDL> test, a[1]
IDL> print, a

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[Message index]

		temporary() problem By: spluque on Tue, 24 September 2013 13:25
		Re: temporary() problem By: David Fanning on Tue, 24 September 2013 13:32
		Re: temporary() problem By: Paul Van Delst[1] on Tue, 24 September 2013 14:29
		Re: temporary() problem By: David Fanning on Tue, 24 September 2013 14:39
		Re: temporary() problem By: spluque on Tue, 24 September 2013 15:43

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