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From: Keith Thompson <kst-u@mib.org>
Newsgroups: comp.lang.ada
Subject: Re: Ada array vs C pointer (call by reference)
Date: 28 Jun 2008 14:18:03 -0700
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Date: 2008-06-28T14:18:03-07:00
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Stephen Leake <Stephe.Leake@nasa.gov> writes:
> Robert A Duff <bobduff@shell01.TheWorld.com> writes:
> > Keith Thompson <kst-u@mib.org> writes:
> >> Interfaces.C.C_Float, which (assuming the Ada implementation gets it
> >> right), is guaranteed to match C's float, or of using Float, which has
> >> no such guarantee (but saves a little typing).  Why would you even
> >> consider using Float?
> >
> > You might have a program that uses Float all over the place,
> > and you want to add some interface to C in one tiny corner
> > of that program.  You might be tempted to use Float at the
> > interface to C in order to avoid a lot of type conversions.
> 
> A better way to avoid a lot of type conversions is to provide a thin C
> interface using Interfaces.C.C_Float, and a thin Ada wrapper that does
> the type conversion to Ada.Float (or some other user provided type).

That will still involve a lot of type conversions at run time, even if
you don't have to write a lot of them in your code.  If Float and
C_Float happen to have the same representation, that's fine.  But if
they differ, then the conversions could have bad numeric consequences.

To summarize:

Programming Is Hard.

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Nokia
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"