Re: Access and alias

[Jeff Carter <jrcarter@acm.org>]

Ted Dennison wrote:
> 
> In article <38EB55AE.D4A241FD@icn.siemens.de>,
>   Alfred Hilscher <Alfred.Hilscher@icn.siemens.de> wrote:
> > If you write your own bindings, you shouldn't work with 'address. Use
> > an in out parameter instead.
> > E.g. proc (ref : SYSTEM.ADDRESS); --> proc (ref : in out X);
> 
> ...unless you are writing a binding to a function, in which case you are
> back to using addresses.

If you have to pass null, access types (with convention C) work fine. If
you don't have to pass null, in out works for procedures, and access
parameters work for functions. All keep the type checking that addresses
lose:

-- int func (int* I);

function F1 (I : System.Address) return Int;
pragma Import (C, F1, "func");

function F2 (I : access Int) return Int;
pragma Import (C, F2, "func");

I : aliased Int;
J : Int;
S : String := Get;

...

J := F1 (I'Address); -- works as intended
J := F1 (S'Address); -- works as not intended
J := F2 (I'access); -- works as intended
J := F2 (S'access); -- compilation error

-- 
Jeff Carter
"You couldn't catch clap in a brothel, silly English K...niggets."
Monty Python & the Holy Grail