Re: problem with abstract types

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

Simon Wright <simon.j.wright@amsjv.com> writes:

> But to make this work you have to do things the right way: the
> "proper" idiom is to initialize using a function,
> 
>    declare
>       Reg : Registry'Class := Open_Registry (...);
>    begin
> 
> where you might need to include some indication of what sort of
> registry to choose in the parameters to Open_Registry. Often people
> use strings. This is a classic example of the Factory pattern ..

Right, but if the code can't figure out the Tag of Reg when it is
created, or if the Tag changes over time, then Reg will have to be of
an access-to-Registry'Class type.  But that does not imply that all
the operations need to take access parameters.  They can take Registry
parameters, and you would then pass Reg.all as the actual parameter.

- Bob