Re: Ada OO Mechanism

[Hyman Rosen <hymie@prolifics.com>]

kilgallen@eisner.decus.org (Larry Kilgallen) writes:
> The fact that GNAT allocates it in one place does not mean all compilers
> will do it in the same place.  Is your question specifically "how does
> GNAT do this ?" ?

I am trying to understand the mechanism behind T'Class. I have been told
that the size of such variables is determined at run-time, and also that
the heap is not required for such variables.

So, to anyone, if you don't mind taking the time to explain, how does
<compiler of your choice> implement this?

Also, I stated in an earlier message that I thought not allowing T'Class
variables in records was not orthogonal, but understandable in light of
the above. Now, suppose I need a function that returns a pair of values,
one of which is a T'Class and the other a boolean. Is there a way to do
this? I can't return a record containing the pair, because I can't have
such a record. I assume that a procedure with a pair of out parameters
won't work, because the T'Class variable which receives the output must
be initialized when declared, and then its tag can't change. So, is there
a way?