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From: Alfred Hilscher <Alfred.Hilscher@icn.siemens.de>
Subject: Re: Access and alias
Date: 2000/04/06
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Date: 2000-04-06T00:00:00+00:00
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Jeff Carter wrote:
> 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

OK. But I would do a little change:

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

Would write
type Int_Access is access all INT;
function F2 (I : Int_Access) return Int;
pragma Import (C, F2, "func");

This avoids some problems that I had with anonymous access types.