Re: GNAT - return by anonymous access

["Randy Brukardt" <randy@rrsoftware.com>]

"Simon Belmont" <sbelmont700@gmail.com> wrote in message 
news:784c67eb-a542-41b0-b23d-fca1234e56b2@n10g2000vbg.googlegroups.com...
>
> This ostensibly simple program prints strange results...
...
>   type test_type (p_obj : access Integer) is limited null record;
...
>   function get return test_type is
>   begin
>      return test_type'(p_obj => new Integer'(42));
>   end get;

You are creating a coextension here. The *language rules* for coextensions 
are full of bugs; we're fixing them virtually every ARG meeting. There is 
little hope for a compiler to get these right in the face of that, beyond 
which doing so is quite expensive.

IMHO, any use of an allocator for an anonymous access type is asking for 
trouble. There is no way to free the memory for such things, and the 
lifetime can easily be extended in various ways, so if the compiler tries 
using a properly local pool for the allocator you end up with a dangling 
poiner. Moreover, they appear to promise something that they cannot deliver 
(heap-based allocation).

Ada 2012 has a restriction No_Anonymous_Allocators; I recommend that all Ada 
programs include and obey this restriction. (Janus/Ada does this by default, 
because we never attempted to use the local pools that supposedly are 
required, and it is better to reject a program rather than implement it 
"wrong".)

                                                    Randy.