Re: Casting from interface type

[Yves Bailly <kafka.fr@laposte.net>]

Adam Beneschan wrote:

>> Using the latest GNAT 2006, I receive the following errors:
>> proc.adb:14:19: invalid tagged conversion, not compatible with
>> type "I'Class" defined at line 3
> 
> Type T is not descended from I, so there cannot be any object in
> I'Class that has type T.

This makes sense to me?

> However, the following should be legal, 
> although GNAT probably won't accept it (see below):
> 
>     var_t := T (T'Class (p));
> 
>> proc.adb:15:21: invalid tagged conversion, not compatible with
>> type "I'Class" defined at line 3
> 
> I think this is legal and GNAT is wrong.  My printed copy of
> 4.6(23.1/2) says that type conversions between *any* two class-wide
> types are legal if one of them has an interface type as its specific
> type, even if the other one doesn't have an interface ancestor, because
> some type in the class *could* have an interface ancestor (as DT does
> in your example).  I tried to check to make sure this section hasn't
> changed since I printed it, but unfortunately www.adaic.com is down
> right now.

Just checked, it hasn't changed since when I downloaded it. This is
this precise clause which made me wondering if I misunderstood
something. Well, maybe I'll fill a bug report...

Thanks for your help.

Regards,

-- 
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