Re: Ada-Singleton-Why does it work like this?

["patrick.gunia@googlemail.com" <patrick.gunia@googlemail.com>]

On 25 Mrz., 12:46, Ludovic Brenta <ludo...@ludovic-brenta.org> wrote:
> On Mar 25, 11:57 am, "patrick.gu...@googlemail.com"
>
>
>
>
>
> <patrick.gu...@googlemail.com> wrote:
> > Yet another question, if my Singleton_Type is unconstrained, why does
> > Ada allow creating Access-Types to unconstrained types allowing to
> > access there record-properties, while not allowing to create an
> > instance of Singleton_Type directly? I thought that Ada demands a
> > declaration of an instance before creating an Access-Type to access
> > it? Maybe I´m mixing in C++, but if I declare a pointer in C++ I
> > either have to create a new instance using "new" in heap-memory where
> > the pointer points to or I have to use references and then let the
> > pointer point to a reference. In both cases I first have to create an
> > object and then let the pointer point to it. When I use access types
> > in Ada in my example it´s possible to create a pointer to a class
> > which can´t be instantiated, because it is unconstrained. Though it
> > works to access the record-properties using the access-type. Could
> > anyone tell me what I´m getting wrong concerning Ada?
>
> > Thank you!
>
> If you want to declare an access type, you do not need an instance;
> you only need a type, which may be unconstrained:
>
> type T (<>) is limited private;
> type Access_T is access T; -- OK
>
> If you want an access *value*, then you do need an object; either one
> from a storage pool, or a pre-existing one:
>
> Access_Value : Access_T := new T'(...);
> -- storage pool. Possible only in the package declaring T, since T is
> private.
>
> Other_Access_Value : Access_T := Access_Value; -- possible anywhere
>
> Neither Access_Value nor Other_Access_Value allow you to see the
> components of T because T is private.
>
> --
> Ludovic Brenta.

Alright, I mixed this up, you´re right. Slowly all pieces make sense
to me and now I´m starting to get the differences and why the
Singleton-implementation works...
Thank you for your help!