Re: Dynamic type system for Ada

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On 24/01/2017 14:58, Victor Porton wrote:
> It seems that you didn't understood me.

You should have asked about data definition layer, not type then. Types 
have operations.

> All I ask is just an Ada type which would be so flexible that could store
> any kind of a value (just like as a variable in a dynamic language).

Task value, protected object value, a value from generic instance not 
yet instantiated, subprogram value?

In languages you have in mind there are types which can be used that way 
and not-so-much-types which cannot.

> This type could be a variant record which could store numbers, lists/arrays,
> strings, etc. (anything that can be stored in a variable in a dynamic
> language).

Then you should have asked about a variant type of some predefined set 
of scalar types and predefined class of containers. It has little use in 
Ada.

As an implementation consider stream attributes. For a stream take a 
memory-located stream. Yes it is implemented in Ada. It has almost no 
use because Ada lacks things I listed. You cannot hang an interface on a 
stream object in order to access the object stored in the stream in the 
same way the original type is accessed (AKA dynamic cast, AKA 
polymorphic object). For this the stream object must inherit the 
interface of the type it contains, and do that ad-hoc. Variant record 
types do the job (dynamic cast is performed by variant selection per 
discriminant), but they are very very limited in what they can do.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de