Re: problem with abstract types

[Ulrich Eckhardt <uli.e@gmx.de>]

David C. Hoos wrote:

>>package registry is
>>   type registry is abstract tagged limited private;
>>   type registry_Access is access all registry'Class;
>>
>>   procedure openRegistry(reg : in out registry; ..) is abstract;
>>   function getRegistry( .. ) return registry_Access
>>   [..]

>>  package registry.unix is
>>     type file_registry is new registry with private;
>>     procedure openRegistry(reg : in out file_registry; ..);  
>>     [..]
>>
>>Any hints what i am missing, or comments how such things are better
>>done in ada?
> 
> This problem has nothing to do with abstract types. The error message means
> exactly what it says.  So, what is the prefix of the "access" attribute?
> It's "reg" so, "reg" must be aliased.

Yes and no ;-). The above fixes the compiler error, but not my
problem.

> All of that being said, the bigger question is "why do you want to take the
> "access" attribute of an access value?

Thats exact my problem. I have no idea how to do it a better way.
I use the package registry as some sort of interface, which sould
make sure that for every instance a set of functions are declared.

But i can not or don't know how to declare an abstract type
and assign later on a real type which is derived from this type.
For example on java i can create an abstract type and also declare
a variable of an abstract type. Later on the programm i can then
instantiate a real type an assign it to this variable. Thats what i
now want to do in java.

Uli
-- 
Ulrich Eckhardt
http://www.uli-eckhardt.de