Re: Flexible Strings (was Equality operator...)

[kaz@vision.crest.nt.com (Kaz Kylheku)]

In article <dewar.862755569@merv>, Robert Dewar <dewar@merv.cs.nyu.edu> wrote:
>So no language standard can meaninfuly specify formal semantiocs for
>what deallocation might mean, beyond specifying that reference to freed
>storage is in an appropriate sense incorrect.
>
>So Ada is no different from C or Pascal or any other lanuage here. I suspect
>that Kevin is not the kind of person who spends his time studying formal
>standards, but if you want to follow this up, for example go look at the
>definition of Dispose in the ANSI Pascal standard.

Actually Ada must be different here. If were were discussing C, we wouldn't
need to generate a week long thread regarding what malloc() and free() are, and
how to use them.

>What does the Ada standard say about Unchecked_Deallocation:
>
>    9  Free(X), when X is not equal to null first performs finalization,
>       as described in 7.6.  It then deallocates the storage occupied by
>       the object designated by X. If the storage pool is a user-defined
>
>
>Nice, but of course deallocate is not really formally defined, then we have
>the implementation advice:
>
>17   For a standard storage pool, Free should actually reclaim the storage.
>
>again "actually reclaim" is not formally defined.
>
>BUT, does this matter in practice? Of course not, all Ada compilers always
>have followed this advice for the standard storage pool, and it would be
>surprising if it were otherwise. This is exactly the same situation as
>observing that all C compilers actualy free storage when free is used.

But the C standard firmly says that ``The free function causes the space
pointed to by ptr to be deallocated, that is, made available for further
allocation'' (ISO 9899:1990 7.10.3.2 The free function). This pretty much
constitutes a requirement that the C implementation actually deallocate
when free is called, which carries more weight than a mere observation
about what all existing implementations do.