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Re: bitwise operators in IDL? [message #25125 is a reply to message #25080]

Tue, 22 May 2001 22:14

marc schellens[1]
Messages: 183
Registered: January 2000

Senior Member

> It would be really nice if IDL had any logical operators, other than
> implied in the ambiguous usage of bitwise op's for different types.
> Specifically, having a "short-circuiting" AND and OR operator set would
> be exceptionally useful.
>
> How often do you find yourself doing something like:
>
> if ptr_valid(a) AND *a ge 0 then...
>
> only to find that it can't work, because AND always evaluates everything
> it operates on. Most decent languages offer short circuiting AND's (and
> OR's etc.), that stop as soon as the true solution is known. Here, if
> ptr_valid(a) is not true, there would be no need to continue to try to
> dereference 'a' (which generates an error), and this snippet would be
> correct.
>
> I guess for now we're stuck with
>
> if ptr_valid(a) then begin
> if *a ge 0 then begin...
>
> Oh the tedium.
>
> JD
To late for short circuitry.
Consider a case when the second function in the if case
has a side effect (e.g. modifying a global variable).
After once defining the language this way, to change it
would mean to introduce incopatibility.

But you can write:
if ptr_valid(a) then if *a eq b then begin
...

which looks a little bit nicer (IMHO).

cheers,
:-) marc

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[Message index]

		bitwise operators in IDL? By: Rick Towler on Fri, 18 May 2001 14:34
		Re: bitwise operators in IDL? By: marc schellens[1] on Tue, 22 May 2001 22:14
		Re: bitwise operators in IDL? By: John-David T. Smith on Wed, 23 May 2001 08:16
		Re: bitwise operators in IDL? By: John-David T. Smith on Tue, 22 May 2001 14:00
		Re: bitwise operators in IDL? By: Stein Vidar Hagfors H[1] on Thu, 24 May 2001 07:14
		Re: bitwise operators in IDL? By: John-David T. Smith on Wed, 23 May 2001 12:46
		Re: bitwise operators in IDL? By: Craig Markwardt on Wed, 23 May 2001 11:19

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