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Re: When Ptr_New doesn't work [message #29018 is a reply to message #28946]

Wed, 23 January 2002 09:27

Richard Younger
Messages: 43
Registered: November 2000

Member

JD Smith wrote:

[...]

> The problem is with IDL's somewhat strict definition of what can
> consititute a "left-hand", or assignable, value. It handles the simple
> case of:
>
> IDL> ((((a))))=1
>
> without choking, but throw anything more complicated at the LHS, and it
> often falls down. It's a known weakness of IDL, revealed in a
> complicated way. ;) One good rule of thumb is that, if the LHS contains
> subscripts, the last character before the "=" (modulo whitespace),
> should be "]" (ok Craig, or ")").

[...]

This seems very strange to me. I think of parenthesis as not modifying
their arguments at all, since they should (in my own little idl, er,
ideal world) change only precedence and not value. Go figure. As you
say, it must be fallout from dynamic typing and/or that incomplete
operator precidence.

I am in the habit of adding parens everywhere I can when constructing
one of those long complicated lines of code from the inside out. I then
make sure the thing works, start from the outside in and remove those
that seem unneccessary. I'm completely suprised I haven't been
frustrated by this quirk before. I guess I must have never put an
outside pair on a LHS, or never noticed the error for something else.

Thanks for clearing things up, JD. It's nice to know why things are
screwy, even if it is "because that's the way they are."

Best,
Rich

--
Richard Younger MIT Lincoln Laboratory
Phone: (781)981-4464 244 Wood St.
Fax: (781)981-0122 Lexington, MA 02421

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[Message index]

		Re: When Ptr_New doesn't work By: badenes on Wed, 23 January 2002 03:43
		Re: When Ptr_New doesn't work By: John-David T. Smith on Tue, 22 January 2002 12:02
		Re: When Ptr_New doesn't work By: badenes on Tue, 22 January 2002 09:38
		Re: When Ptr_New doesn't work By: Richard Younger on Tue, 22 January 2002 09:36
		Re: When Ptr_New doesn't work By: Malcolm Walters on Tue, 22 January 2002 06:51
		Re: When Ptr_New doesn't work By: Richard Younger on Wed, 23 January 2002 09:27

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