From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-1.3 required=5.0 tests=BAYES_00,INVALID_MSGID
	autolearn=no autolearn_force=no version=3.4.4
X-Google-Language: ENGLISH,ASCII-7-bit
X-Google-Thread: 103376,30047505e1b73aa8
X-Google-Attributes: gid103376,public
From: Matthew Heaney <matthew_heaney@acm.org>
Subject: Re: Access conversions
Date: 1998/10/12
Message-ID: <m37ly6vdqj.fsf@mheaney.ni.net>#1/1
X-Deja-AN: 400153188
Sender: matt@mheaney.ni.net
References: <x7v1zoe73ec.fsf@pogner.demon.co.uk>
NNTP-Posting-Date: Mon, 12 Oct 1998 00:07:09 PDT
Newsgroups: comp.lang.ada
Date: 1998-10-12T00:00:00+00:00
List-Id: <comp.lang.ada>

Simon Wright <simon@pogner.demon.co.uk> writes:

> I need to write a function
> 
>   function Is_Member (G : Graph'Class; V : Vertex'Class) return Boolean;
> 
> where there is a type
> 
>   type Graph_Ptr is access all Graph'Class;
> 
> and a Vertex has a component Rep with a component Enclosing of type
> Graph_Ptr which accesses its enclosing Graph.
> 
> In GNAT I can say in Is_Member
> 
>       return V.Rep.Enclosing = G'Unrestricted_Access;
> 
> but of course this isn't portable.
> 
> If I say
> 
>   function To_Ptr is new Ada.Unchecked_Conversion (System.Address,
>                                                    Graph_Ptr);
> 
> and then in Is_Member
> 
>       return V.Rep.Enclosing = To_Ptr (G'Address);
> 
> which appears to work as expected in GNAT and ObjectAda 7.1, am I in
> fact riding for a fall?
> 
> -Simon

Instead of converting the address to an access type, and then comparing
access types, why not compare addresses directly:

   return V.Rep.Enclosing.all'Address = G'Address;

Isn't this portable?