Re: Interfaces.C.Strings chars_ptr memory management strategy

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

"Alejandro R. Mosteo" <alejandro@mosteo.com> wrote in message 
news:peoj3f$8ti$1@dont-email.me...
> On 30/05/2018 21:56, Randy Brukardt wrote:
...
>>> Is the in-place built limited tagged type guaranteed to live during the
>>> call to the C function? (In other words, is the pointer safe (as long as
>>> the C side does not make a copy, of course)?
>>
>> That depends on the master of the parameter. I believe that the master of 
>> a
>> parameter is that of the call (each call being it's own master for the
>> parameters) -- you'd have to look in 7.6.1 to be sure. So they stay 
>> around
>> as long as the call.
>
> Might that be 6.4.1? 7 deals with packages (in 2012).

No. The rules for masters are defined with finalization in 7.6, and 
specifically in 7.6.1(3/2). The single middle sentence in that paragraph (a 
classic RM run-on sentence) defines completely where every object in an Ada 
program is finalized -- and also defines large parts of the accessibility 
and tasking models (which mainly follow the same master rules).

> Although it was too dense for me anyway :(

That's why I didn't want to give you a definitive answer. It takes a lot of 
mental effort to do that, and I need to save that effort for things people 
pay me to do. ;-)

...
>>       Foo (Bar (Ugh (...))
>>
>> The result of Ugh is finalized when the call to Bar ends, so if it is
>> somehow in the result of Bar, you could get trouble in Foo. You can avoid
>> that by declaring the parameter "aliased" (those belong to the *result* 
>> of
>> the function, so they stick around longer).
>
> The parameter is actually aliased already. So I hope your impressions are 
> right and I'm on firm ground then, a pleasant surprise.

Turns out I was wrong: 7.6.1(3/2) says that only the outer function call is 
a master. So there is no problem in even the case I suggested.

                                                   Randy.