Re: Libraries written in Ada

[Martin Krischik <martin@krischik.com>]

Thomas Lotze wrote:

> On Mon, 22 Nov 2004 18:59:16 +0100, Martin Krischik wrote:
> 
>> Actually both. The common runtime consists of packages as well and every
>> package may or may not have it's own mini runtime environment. There are
>> pragma instructions to controll that i.E. "pragma Pure" says that a
>> package has no runtime environment and does not use another package with
>> a runtime environment.
> 
> And even though it is thus possible to have an Ada package which doesn't
> need a runtime environment, it is always necessary to initialize one? Is
> that what you meant by "it's not an optional extra" in one of your
> earlier messages?

Consider the following package:

package body
   Test
is

  Y : Integer;

  procedure X 
  is
  begin
    Y := 1;
  end X;

begin
  X;
end Test;

In this case "Y" is the runtime environment and unless you have activated
very agressive optimization the procedure X need to called at package
elaboration.

Of corse:

package body
   Test
is

  Y : Integer := 1;

end Test;

can be preelaborated by the compiler and then no runtime elaboration is
needed.

>> Please Note: you are asking very low level questions. Normaly you don't
>> need to worry about it. Ada as a package orientated language has it all
>> build.

> Sure, but I'd like to know what implications my choice of language has for
> using the library I want to write before I lean back and feel happy about
> leaving these details to the language.

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.

>> That's the normal way for static linking. It does have the advantage that
>> the binder will bind and elaborate only the packages which are actually
>> used.

> Nice.
 
> Thanks for your explanations so far. One thing I haven't thought about
> asking yet: What does adafinal() normally do? Does it things like flushing
> file buffers and closing files, or is it just about cleaning up memory?
> So, if it is the last function called from main(), may it just as well be
> omitted?

Ada95 is a object orientated language with some form contructor/descructor
system called controled objects. adafinal () will call the finalisation for
static controled objects.

With Regards

Martin

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