Re: limited private types, "=" operator

[mackey@scs.fiu.edu]

In article <1152@cs.nps.navy.mil> erickson@cs.nps.navy.mil (David Erickson) writes:
>Is there any way to define "=" for a limited private type which is an
>access type (which may be null)?  The problem arises trying to test for
>null without producing an infinitely recursive definition.
>
>The only solution that I am aware of is to use UNCHECKED_CONVERSION to
>retype the access type during the test for null, but this is a hack.
>Is there a cleaner solution?
>
>Thanks -
>
>	Dave Erickson

The easiest way to solve this problem is not to say
    type blurg is limited private
    ...
    type blurg is access widget;
at all.  Instead, say:
    type blurg is limited private
    ...
    type blurg_pointer is access widget;
    type blurg is record
            value : blurg_pointer;
         end record;

Then, when you want to deal with the procedure call "=" which
compares blurgs, you use the record.  Inside the body of the package,
you qualify the object with the .value field and you then get the
"=" which compares the pointers themselves.  The client of this
package of course can not get to this function.

.