Re: Limited initialization for non-limited types

[Robert A Duff <bobduff@shell01.TheWorld.com>]

Eric Hughes <eric.eh9@gmail.com> writes:

> Is there any way of getting in-place initialization for non-limited
> objects?

No.

We're thinking about doing that in GNAT as an optimization,
but there's no way to force it.  Note that assignment
statements cannot use build-in-place in all cases.

Perhaps you can get what you want by wrapping a nonlimited type in a
limited record?

> So here's the problem.  I can't trace the Initialize call
> "correctly".  Consider the obvious initialization:
>
>     T : Trace ;
>     A : X := Construct_X( T ) ;
>
> Because X is not a limited type, this code translates thus (in one
> ordering):
>
>     T : Trace ;
>     A : X ;
>     Initialize( A ) ;
>     Temp : X := Construct_X( T ) ; -- as if limited, constructed in
> place
>     Initialize( Temp ) ; -- (*)
>     Finalize( A ) ;
>     A := Temp ;
>     Adjust( A ) ;
>     Finalize( Temp ) ;

That's not a correct translation.  For example, the line marked (*) will
overwrite the result of Construct_X.

To see what GNAT actually generates, use the -gnatD or -gnatG switch.
But there's no guarantee it won't change in future versions!

- Bob