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From: mg@asp.camb.inmet.com (Mitch Gart)
Subject: Re: Invoking parental methods (was: Java vs Ada 95)
Date: 1996/11/06
Message-ID: <E0GAKr.HB.0.-s@inmet.camb.inmet.com>#1/1
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Date: 1996-11-06T00:00:00+00:00
List-Id: <comp.lang.ada>


Tucker is right.  But here's a slightly different example, which
shows the problem where a type conversion of an access type doesn't
do what might be expected.  The difference is that super is a
classwide access type.

    with ada.text_io; use ada.text_io;
     
    procedure supertest is
	package p1 is
	    type parent_obj is tagged null record;
	    type super is access all parent_obj'class;
	    procedure p_first (param: access parent_obj);
	end p1;
	package body p1 is
	    procedure p_first (param: access parent_obj) is
	    begin
		put_line("parent p_first");
	    end;
	end p1;
     
	package p2 is
	    type child_obj is new p1.parent_obj with null record;
	    procedure p_first (param: access child_obj);
	end p2;
	package body p2 is
	    procedure p_first (param: access child_obj) is
	    begin
		put_line("child p_first");
		p1.p_first(p1.super(param));	-- ***
	    end; 
	end p2;
     
	child: aliased p2.child_obj;
    begin
	p2.p_first(child'access);
    end;

The line marked *** dispatches back to p2.p_first, causing an
infinite recursion.  To get this one to do what's wanted, the
notation

    p1.p_first(p1.parent_obj(param.all)'access);

is needed.

- Mitch