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Newsgroups: comp.lang.ada
Date: Sun, 28 Jul 2013 14:13:22 -0700 (PDT)
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Subject: Re: System.Address to Access to function/procedure conversion
From: Shark8 <onewingedshark@gmail.com>
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Xref: news.eternal-september.org comp.lang.ada:16588
Date: 2013-07-28T14:13:22-07:00
List-Id: <comp.lang.ada>

On Sunday, July 28, 2013 1:05:44 PM UTC-6, Tarek Ghaleb wrote:
> On 2013-07-28, Dmitry A. Kazakov wrote:
> 
> > If you pass anything to C you should better keep it under C convention,
> > even if you are certain that C does not touch it. You should pass an
> > access-to-procedure/function to C and get it back. The access type will
> > have pragma Convention (C, ... set. You don't need address here. E.g.
> 
> I agree completely. Using C convention is the way to do it. But is it
> *possible* to call a function using its address? (even if not a such a
> great idea)

Yes. It's actually absurdly easy. Here's a sample of how to do it in Ada 2012, the same will work in earliet versions of Ada using Pargmas... all the way back to 83, IIUC.

    -- Used a declare-block for expedience; I had a test-bed file open.
    -- Be sure to WITH System.

    ACTUAL_TEST:
    declare

	Procedure K with Convention => C;
	Procedure K is
	begin
	    Ada.Text_IO.Put_Line( "K was called" );
	end K;
	
	Procedure Execute( Addr : System.Address ) is
	    Procedure Stub with Import, Convention => C, Address => Addr;
	Begin
	    Stub;
	End Execute;
	
    begin
	Execute( K'Address );
    end ACTUAL_TEST; 

And there you are.