Re: Access conversions

[Matthew Heaney <matthew_heaney@acm.org>]

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?