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From: "Jeffrey R.Carter" <spam.jrcarter.not@spam.acm.org.not>
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Subject: Re: strange cursor in nested containers
Date: Tue, 9 May 2023 10:36:33 +0200
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On 2023-05-09 05:56, Randy Brukardt wrote:
> It's not required to detect such cursors because it is expensive to do so
> perfectly (essentially, each cursor has to be controlled and one has to keep
> a list of them associated with the container). There are imperfect solutions
> which are likely to be "good enough" in practice, but they still have a
> (small) cost which may be an issue for some uses. Thus, most implementers
> don't use them. I know the original GNAT containers had a debugging version
> that included such checks, but I don't know if they still exist or how one
> would enable them if they do.

This cost is due to the decision to allow access to elements using only a 
cursor. If both the container and the cursor are needed, then the cost is 
significantly reduced. This is the approach that was used in the Ada-95 version 
of the PragmAda Reusable Components.

-- 
Jeff Carter
“Bug rates in C++ are running higher even than C ...”
Stephen F. Zeigler
216