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Date: 5 Oct 92 02:33:12 GMT
From: alex@MIMSY.CS.UMD.EDU  (Alex Blakemore)
Subject: Re: Ada question: access types
Message-ID: <60887@mimsy.umd.edu>
List-Id: <comp.lang.ada>

In article <1992Oct4.211734.9047@seas.gwu.edu> nreich@seas.gwu.edu (Norman Reic
h) writes:

Assume
package my_types is

>      TYPE ptr IS ACCESS node;
>      TYPE node IS
>        RECORD
>          name ...
>          ...
>          nextn :ptr;
>        END RECORD;
>      nl :ptr;

and in another library unit 
>      if (nl = NULL) then          --error at this line
>      type clash in parameter to "="

type ptr is probably in a different package than the if statement.
you probably made type ptr visible via a with clause and did not
make it _directly_ visible via a use clause.  this is probably the
most common "error" new users hit and Ada9X is more forgiving here.
The error message could be better though.

Remember the function "=" (left, right : ptr) is implicitly
defined just after the definition of type ptr.

Your choices are:
a. invoke "=" using dotted infix notation.
   if my_types."=" (nl, null) then
b. make my_types."=" directly visible by adding a use clause.
   use my_types;
c. rename my_types."=" to make it directly visible
   function "=" (left, right : my_types.ptr) renames my_types."=";
-- 
---------------------------------------------------
Alex Blakemore alex@cs.umd.edu   NeXT mail accepted