Re: How to get Ada to ?cross the chasm??

[Niklas Holsti <niklas.holsti@tidorum.invalid>]

On 18-05-11 01:52 , Paul Rubin wrote:
> "Randy Brukardt" <randy@rrsoftware.com> writes:
>> No wonder you don't understand: Ada 95 had none of the container stuff or
>> other features that reduces the memory management burden without using GC.
>> At a minimum, you need to consider Ada 2005, but the most recent Ada is
>> best.
>
> Ah, ok, I was also going by
>
>   http://cowlark.com/2014-04-27-ada/index.html
>
> which claims Ada has no standardized way to release allocated memory (so
> each implementation had its own way).

That summary of Ada has many inaccuracies, but mostly minor ones. Pity 
that they have not been corrected (some of the examples are 
syntactically wrong, too).

For releasing allocated heap memory, Ada.Unchecked_Deallocation is just 
as standard as "free" in C. People are just scared by the name, and by 
the asymmetry between the simple, primitive "new" keyword and the long 
library-level name Unchecked_Deallocation.

Logically, perhaps Ada should not have included a "new" keyword to 
allocate heap memory, but should have had something like a generic 
library function Ada.Unchecked_Allocation, which is "unchecked" in the 
sense that there is no guarantee that the allocated memory will be 
released when no longer needed. I can imagine the confusion that would 
have caused...

> If you can suggest a good place
> to read about the current standard method I'd appreciate it.

The idea is just to use the standard containers, including the ones that 
can handle indefinite types like String, instead of doing "new" and 
Unchecked_Deallocation yourself. And to use cursors pointing to elements 
of a container, instead of using visible access types. The containers 
then manage the heap allocations and releases.

However, I don't think this method will free you from worrying about 
dangling references -- I believe a cursor can be left dangling, just as 
an access value can be. (I haven't yet had occasion to do such 
container-centric Ada programming, although I have used the Ada 
containers in less central roles.)

-- 
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
       .      @       .