Re: How to properly clean up an extended, generic structure?

["jimmaureenrogers@worldnet.att.net" <jimmaureenrogers@worldnet.att.net>]

Peter C. Chapin wrote:
> I've created a procedure Destroy_Tree that uses an instance of
> Ada.Unchecked_Deallocation to remove all the nodes in a given tree.
> Destroy_Tree is meant to be used when a tree is no longer needed and it
> serves the role of a destructor (using C++ terminology). It occurs to
> me, though, that Item_Type might have its own clean up needs. I assume
> that Unchecked_Deallocation knows nothing about that. Thus my code
> currently might be improperly cleaning up the Item_Types in each tree
> node. In C++ this is not a problem because deleting a node invokes the
> node's destructor (if there is one) so the issue is handled
> automatically. My question is how do I best deal with this in Ada?
>
> I could pass a clean up procedure for Item_Types as another generic
> parameter. However, in cases where no such procedure is necessary (for
> example, when Item_Type is just Integer), such a solution seems awkward.
> Is there a nicer solution?

You should read up on Ada controlled types. The tree itself can be a
controlled type. The tree elements may or may not be controlled types.

Ada controlled types allow you to specify actions to be taken upon
initialization, adjustment, and finalization of a data element. These
actions effectively mimic many of the characteristics of C++
constructors and destructors.

Jim Rogers