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Re: Would you consider this a bug? [message #13067 is a reply to message #12982]

Thu, 01 October 1998 00:00

David Kastrup
Messages: 33
Registered: February 1998

Member

Kevin Ivory <Kevin.Ivory@linmpi.mpg.de> writes:

> David Kastrup wrote:
>> a=[3,4,5]
>> a[[2,1,0]] = a
>>
>> a will be set to [3,4,3]
>>
>> Would you think this a bug?
>
> I think this is extremely dangerous programming: you might get
> undefined or unpredictable results with almost any programming language
> in this type of case.

Disagree. IDL is WRT to assignment a value oriented language, so one
might expect first the right side to be evaluated and then the left
side to be assigned (unless IDL can do this more efficiently without
affecting the result).

If I really wanted a to be destroyed during the operation, I could
have written
a[[2,1,0]] = temporary(a)

> The clean way of doing what you want is to
> index the right side of the expression:
> a = a[[2,1,0]]

Unfortunately, translating something like

a[[5,2,3,0,4,1]] = a
into the equivalent
a = a[[3,5,1,2,4,0]]
is not easy to do in the general case. In my particular case, I had
some data that needed to be processed in sorted order, the results
needed to be rearranged in original order.

Something like
s = sort(a)
a = a[s]
process(a)
a[s] = a

--
David Kastrup Phone: +49-234-700-5570
Email: dak@neuroinformatik.ruhr-uni-bochum.de Fax: +49-234-709-4209
Institut fï¿½r Neuroinformatik, Universitï¿½tsstr. 150, 44780 Bochum, Germany

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[Message index]

		Would you consider this a bug? By: David Kastrup on Wed, 30 September 1998 00:00
		Re: Would you consider this a bug? By: David Kastrup on Mon, 05 October 1998 00:00
		Re: Would you consider this a bug? By: muswick on Sat, 03 October 1998 00:00
		Re: Would you consider this a bug? By: Martin Schultz on Fri, 02 October 1998 00:00
		Re: Would you consider this a bug? By: David Kastrup on Thu, 01 October 1998 00:00
		Re: Would you consider this a bug? By: korpela on Thu, 01 October 1998 00:00
		Re: Would you consider this a bug? By: Kevin Ivory on Thu, 01 October 1998 00:00
		Re: Would you consider this a bug? By: David Kastrup on Thu, 01 October 1998 00:00
		Re: Would you consider this a bug? By: Kevin Ivory on Thu, 01 October 1998 00:00

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