Re: Libraries written in Ada

[Martin Krischik <martin@krischik.com>]

Thomas Lotze wrote:

> On Tue, 23 Nov 2004 10:48:45 +0100, Martin Krischik wrote:
> 
>> can be preelaborated by the compiler and then no runtime elaboration is
>> needed.
> 
> How can I find out whether the code produced by the compiler (not a
> specific one, but any compiler that conforms to the spec) needs runtime
> elaboration? Are there simple rules such as "this code pattern may or does
> require runtime elaboration while that pattern can be safely assumed to
> work without"? I'd have to dig further through the references, but I
> haven't found a clear statement so far.

You can restrict packages to not use specific elaboations:

pragma Pure ();
pragma Preelaboreate ();

The pragmas are for the Annex E where these things are more important than
in normal development.

>> If you like low leve: I the excample above the GNAT compiler will create
>> a "package X init" procedure and a Boolean "package X initilized" (I
>> could find out the actual names - but I don't think it is needed).
>> adainit () will check the boolean and call procedure when needed.
> 
> So it's not possible to reset a package in the midst of program execution?
> If so, is it a conscious design decision, and what's the rationale? (The
> solution seems to be offering reset functionality in the package.)

A conscious design decision:

package 
  Test
is

   Y : constant Integer = X (...);

end Test;
 
Do I have to explain it or do you spot it yourself ;-) .

>> Ada95 is a object orientated language with some form
>> contructor/descructor system called controled objects. adafinal () will
>> call the finalisation for static controled objects.
> 
> What if a package doesn't have any specific finalization code? Is there
> some generic stuff that must always be run, or can finalization be omitted
> in such a case?

With GNAT the binder will automaticly generate the needed code just like
with adainit ().

The code generated by the binder is stored in some b~ file. It is a normal
Ada source code. In Ada only programms the binder output is deleted
imediatly after linking - in mixed language development the binder output
is not deleted. More over: you can choose Ada or C as bind language -
whatever suits you best.

BTW: That's where I got my knowledge from: I did make an Ada library for use
with C (http://cvs.sourceforge.net/cgi-bin/viewcvs.cgi/adacl/CUnicode) and
had more then one good look at the binder output.

And to be honest: While it is possible to write Ada code that does not need
any init or term - you won't have much fun doing so. i.E.

package Interface.C is Pure but
package Interface.C.Strings is only Preelaborate and
package Ada.Text_IO is unmarked.

And if a package is unmarked then you have to expect both init and term.

With Regards

Martin
-- 
mailto://krischik@users.sourceforge.net
http://www.ada.krischik.com