Re: S-expression I/O in Ada

[Georg Bauhaus <rm.dash-bauhaus@futureapps.de>]

On 13.08.10 10:56, Natacha Kerensikova wrote:

> Ada arrays are statically sized,

Not quite, but I think you mean that once an array is allocated, you
can't add more components than are declared by the index constraint?
Example:

procedure Uses_Array (N : Positive; ...) is

   X : array (1 .. N) of Character;  -- now fixed to N compoments

begin...

But Ada's Container packages can provide for the desired flexibility.
There are containers of homogeneous components and containers of
heterogeneous components.  The latter have _Indefinite in their
package's names.  Example:

 package Vecs is new Ada.Containers.Indefinite_Vectors
     (Element_Type => Types.Heterogenous'Class,
      Index_Type => Positive,
      "=" => Types.Eq);

(Vecs.Vector objects will grow as needed.)

Another option is to instantiate a "definite" container generic with
a pointer type, which is definite.  Its access values will point
to any object in some hierarchy.  (This can mean pointers to
any objects that share the same interface (Ada 2005 keyword),
so types need not even be rooted at the same one parent type,
I think). For example

   package S_Lists is new Ada.Containers.Doubly_Linked_Lists
     (Element_Type => Some_Hier_Ptr,
      "=" => ...);


Georg