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Date: Sun, 09 Jul 2006 09:42:18 -0400
From: "Peter C. Chapin" <pchapin@sover.net>
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Newsgroups: comp.lang.ada
Subject: How to properly clean up an extended, generic structure?
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Date: 2006-07-09T09:42:18-04:00
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Hello! I'm working on improving my Ada skills by assigning myself little 
programming exercises and then solving them in Ada. I come from a C++ 
background so I tend to see the world in C++ terms. I realize that isn't 
necessarily helpful.

Right now I'm working on a generic package that implements splay trees. 
My generic parameters look like:

generic
    type Item_Type is private;
    with function "<"(L : Item_Type; R : Item_Type) return Boolean;
package Splay_Tree is ...


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?

Peter