Re: GNAT 4.2.3 Ubuntu reports weird compile error wrt Unchecked_Access

[Jerry <lanceboyle@qwest.net>]

Thank you for your comments, but they don't exactly apply to my
question.

The code snippet that I gave, though brief, shows the use of
'Unchecked_Access. I used it precisely to overcome the accessibility
rules ("Access-Type Lifetime Rule" in the terminology of Cohen, "Ada
as a Second Langugage").

As I understand it, the compiler should not have issued the error that
it did, and in fact on two of the compilers mentioned in my original
post, it did not issue the error. The error should only be issued, in
this case, when 'Access is used, and in fact, it is issued.

The compiler in question seems to have issued a spurious error
message.

Jerry

On Aug 16, 10:59 pm, a...@anon.org (anon) wrote:
> If the GNAT compiler follows the RM on "accessibility" rules.  Then it
> will force you to use the "Unchecked_Access" attribute for any non-local
> pointer trying to point to local object".  Solution: If possible move the
> object to be access to a package global variable (non-local), then you can
> use Access attribute.
>
> Note:
> RM 13.10 (1) => "The attribute Unchecked_Access is used to create access
> values in an unsafe manner -- the programmer is responsible for
> preventing 'dangling references.' "
>
> In <7053ea09-38cd-4e30-9827-a1384bafd...@p31g2000prf.googlegroups.com>, Jerry <lancebo...@qwest.net> writes:
>
> >I have a curious report from two members of the development team for
> >PLplot, a popular plotting package for which I have written bindings
> >in Ada. The project is mature enough that the team decided to enable
> >Ada by default when building, so I am concerned about the following e-
> >mail.
>
> >========== begin e-mail ============
>
> ><First comment from team member>
>
> >This latest change to the Ada bindings causes a build error for me
> >with gnat 4.2.3 on Ubuntu.
>
> >plplot.adb:2751:37: non-local pointer cannot point to local object
> >The offending line is
> >    PL_Pen_Labels(Index) := Temp_C_String'Unchecked_Access;
>
> ><Response from another team member>
>
> >This must depend on the version of gnat since I don't see this error
> >for gnat 4.3.1-2 from Debian testing (and I presume Jerry didn't see
> >it for his gnat-4.3 version as well).
>
> >========= end e-mail ==============
>
> >I (Jerry) in fact did not see a problem on my OS X 4.3 compiler.
>
> >I could supply more details of the code and might even try to write a
> >small program but testing on someone else's machine would be a bit
> >tedious. BUT--this error makes no sense to me--I would expect to (and
> >_do_) see this error if the line in question is
>
> >    PL_Pen_Labels(Index) := Temp_C_String'Access;
>
> >The whole purpose of using Unchecked_Access is to make this error go
> >away. It this a known problem on 4.2.3 Unbutu? Is it a compiler error?
> >Why does it work as expected on my 4.3 OS X, on 4.3.1-2 Debian
> >testing, but not 4.2.3 Ubuntu?
>
> >Jerry