Re: Issue with GNAT GPL 2009 and GtkAda

[Stephen Leake <stephen_leake@stephe-leake.org>]

Damien Carbonne <damien.carbonne@free.fr> writes:

> Stephen Leake a �crit :
>> The problem is clear here.
>>
>> "D : in out Derived" is allowed to create a copy of the actual
>> parameter. Thus the 'Access in Foreach could be on a stack copy of D,
>> which will disappear eventually, leaving a dangling pointer in BB. So
>> the accessibility error is correct.
>>
>> ...
>
> If what you say is true, why does the following example work fine
> (using GNAT), without any compiler warning or execution error ?

Because the object being passed is explicitly labeled "aliased"; that
means 'Access is allowed. See my other post from today.

> As I told in a previous message, I don't want to change the "in out"
> mode of Interface (representing the code I wrote and that is
> independant of GtkAda or any graphical toolkit), because one day it
> could be used in cunjunction with third party code that uses access
> ! Otherwise, it would almost certainly mean that one needs to use
> access almost everywhere, even if it is meaningless.

It's not meaningless. It tells the user that the body needs an access
value. 

Hmm. I guess you mean "If I use a backend (other than GtkAda) that
doesn't require access values, the use of 'access' in my frontend
would be meaningless".

Yes, that's true. Or at least, it only tells the user "if you switch
to some other backend, that might need an access value".

It's the price you pay for supporting multiple backends; you must
support the worst feature of the entire set :).

-- 
-- Stephe