Re: GNAT 4.2.3 Ubuntu reports weird compile error wrt Unchecked_Access

[anon@anon.org (anon)]

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-a1384bafd190@p31g2000prf.googlegroups.com>, Jerry <lanceboyle@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