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From: Robert A Duff <bobduff@shell01.TheWorld.com>
Newsgroups: comp.lang.ada
Subject: Re: This can't be done in Ada...or?
Date: 15 Feb 2005 08:41:26 -0500
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Date: 2005-02-15T08:41:26-05:00
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Jacob Sparre Andersen <sparre@nbi.dk> writes:

> Mark Lorenzen wrote:
> > "Per Lindquist" <commander@death-star.com> writes:
> 
> > > One of our target environments is a time-critical real-time
> > > system. We are worried about the execution overhead implied by a
> > > package instantiation (or any 'new' statement) in every subprogram
> > > in the system.
> > > 
> > > Will your solution cause overhead for each subprogram call?

Probably.

> > A compile-time instantiation of a package has nothing to do with
> > run-time efficiency. You can also define a new type in a subprogram,
> > which doesn't affect run-time efficiency either.
> 
> Aren't the compilers (theoretically) allowed to delay the
> instantiation of the packgage until run-time?

No, instantiation is a compile-time concept.  I'm not sure what
it would mean to delay it until run time.

The issue here is the cost of running the elaboration code of the
instance.  Theoretically, the compiler could optimize it away in this
case, but I don't think any Ada compilers are that smart.  The only
way to know for sure is to try it.

This Reflection package has a bunch of string manipulation code,
and if you instantiate it in a procedure, it will happen
every time that procedure is called (unless the compiler
is smarter than I think it is).  This could indeed be very
costly.

- Bob