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From: "Ayende Rahien" <Dont@spam.me>
Newsgroups: comp.lang.ada
Subject: Problem trying to implement generics.
Date: Wed, 11 Apr 2001 17:04:22 +0200
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Date: 2001-04-11T17:04:22+02:00
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I've just started to learn Ada, and I've some problem solving some problems.

Here is the spec I'm trying to compile:

with Ada.Finalization;
generic
 type data_type is private;
 type Sort_by is private;
package Binary_Trees is
 type binary_Tree is new Ada.Finalization.controlled with private;
 type node is private;
 type node_access is access all Node;
 type data_access is access all Data_type;
 procedure insert(insert_this : in data_type; Sort : in sort_by);
 --Insert into the binary tree, sort according to sort.
 function Delete(Delete_this: in Sort_by; Index : in natural := 1) return
boolean;
 -- Delete a node from the tree, return true if succeeded, return false if
 -- the node does not exist.
 function Get(Search_For: in sort_by; index : in natural := 1) return
data_access;
 -- Search for nodes with duplicate sort_by variable. It find the first
 -- node with the sort_by equal to the given one, and then continue to check
for Index
 -- number of duplicated. It return null if it there isn't a suitable node
in the
 -- correct index.
 private
  type Binary_Tree is new Ada.Finalization.controlled with record
   root: Node_access := null;
  end record;
  type node is record
   Data : Data_type;
   Sorted_by: Sort_by;
   Parent, Left, right : Node_access;
  end record;
     procedure Adjust(Object : in out Binary_Tree );
     procedure Finalize(Object : in out Binary_Tree );
end Binary_Trees;

I trying to put the defination of Node in the body, but it results in
compilation error, is there some way to put the defination in the body? Or
does it matter naught, because it's on the private part of the package?

Since it's a binary tree, I've to have > working on all types that sort_by
work on.
How do I force it?
At the moment, I've three compilation errors when I'm trying to use > on
sort_by data.
Here is the error:
bintree.adb: Error: line 43 col 25 LRM:8.4(1), Binary operator ">" between
Sort_by and Sort_by not directly visible, use clause or conversion might be
needed

This line also result in an error, and I don't know why:
procedure insert(insert_this : in data_type; Sort : in sort_by) is
Here is the error this line produce:
bintree.adb: Error: line 107 col 12 LRM:3.11.1(7), subprogram body is a
homograph of another subprogram which does not require a completion,
continuing

I also have this function:
 function Get(Search_For: in sort_by; index : in natural := 1) return
data_access is
  result : node_access := find(search_for,index);
 begin
  if result = null then
   return null;
  else
   return result.data'access;
  end if;
 end get;

find return a node_access, get translate it to data_access, I tried using
'access tag to make it return data_access, but it didn't qute work.
Here is the error:
bintree.adb: Error: line 150 col 18 LRM:3.10.2(23&31), The prefix to 'ACCESS
must be either an aliased view of an object or denote a subprogram with a
non-intrinsic calling convention, Continuing

Also I've a trouble using Root variable in a function that is undefied in
the spec (Find function).
I suppose I could put it in the private part, but can it be avoided?
Here is the error I got:
bintree.adb: Error: line 8 col 28 LRM:4.1(3), Direct name, root, is not
visible, Ignoring future references

Thanks in advance,
Ayende Rahien