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Date: Wed, 8 Nov 2017 21:37:42 -0800 (PST)
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Subject: Comparing Access Types
From: Jere <jhb.chat@gmail.com>
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Xref: feeder.eternal-september.org comp.lang.ada:48777
Date: 2017-11-08T21:37:42-08:00
List-Id: <comp.lang.ada>

I have a package which uses a type to wrap an access type.  I thought it
might be nice to provide the basic comparison functions, "=", "<", ">", etc.
but access types can only be compared using "=" and "/=".  I figured that
way, my types could be used in some sort of sorted container, like a map.

I want to keep the incomplete type for other reasons, so that seems to limit
my options.

1.  Address_To_Access_Conversions is out (cannot use an incomplete type)
2.  I cannot simply do var.all'Address (Again, incomplete type)

Is there some way to do this within the Ada standard or am I hamstrung
due to the incomplete type specification?

Also, why weren't <, >, <=, >= provided for access types.  Even if the
representation of an Access type is implementation defined, surely
those operators could have been defined.

A toned down example:

generic
   type Item_Type(<>);
   type Item_Access is access Item_Type;
package My_Package is

   type Some_Type is record
      Reference : Item_Access := null;
   end record;

   function "<" (Left,Right : Some_Type) return Boolean;

end My_Package;

package body My_Package is

function "<" (Left,Right : Some_Type) return Boolean is
begin
   return Left.Reference < Right.Reference;  --fails to compile
end "<";

end My_Package