Re: Constructors with multiple inheritance

["Rego, P." <pvrego@gmail.com>]

> Because null cannot be dereferenced. If you want null allowed you have to
> declare it as:
>    function Construct (Object_Reference : access Parent_Class)
>       return Parent_Class_Ptr;
> or
>    function Construct (Object_Reference : Parent_Class_Ptr)
>       return Parent_Class_Ptr;
> The first variant is a "method" of Parent_Class in the first argument. The
> second variant is not.

Maybe it's a good idea :-) . The first variant I guess could fit me very well, and I did not think about it before.
 
> Technically you cannot inherit class. Class is a set of types closed upon
> derivation. When you derive type S from type T, then S and T are members of
> the class rooted in the type T. S inherits operations etc from T.
> What in C++ is called class is in Ada a tagged type and/or a class-wide
> type, because C++ fails to distinguish them.
> 1. In Ada access is based on visibility, which in turn rely on the packages
> structure, not types.
> 2. Inheritance and overriding is related to tagged types. You can always
> derive from a type which view is tagged. (A type can be privately tagged,
> but publicly not, from this type you cannot derive)

Ok. I follow you.

> Prefix notation works only if you have the first argument of tagged type.
> The questions are why do you need an argument which is null? Why do you
> need access types at all. It does not look how things are usually done in
> Ada.

Well, I'm trying to implement a kind of finite group for using with an AI algorithm. So I need to construct an empty queue (filled when the system starts) which points to other types of empty queues but which are been filled when the system learns.
 
> >> What is wrong with the abstract factory pattern?
> > 
> > Nothing wrong. I'm not questioning this.
> 
> So why don't you use it?
A good point. No reason at all. Maybe it can simplify some things.
--
Dmitry and Bob, thank you for always helping me in my Ada learning. I'm very grateful (for you and others I did not cite here or the list would be very long).