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From: Rakesh Malhotra <rakesh.malhotra@pop.safetran.com>
Subject: Re: PRECOMPILATION
Date: 1999/02/18
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 <36C0B5D4.DEF83A66@averstar.com> <7ahor8$otv@news1.newsguy.com>
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Newsgroups: comp.lang.ada
Date: 1999-02-18T00:00:00+00:00
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Samuel Mize wrote:
> 
> Tucker Taft <stt@averstar.com> wrote:
> You'll have to provide
> some higher-level package that interacts with the system, instead
> of just embedding code to do low-level system things throughout
> your program....
>
> C-experienced people probably expect platform-specific issues to be
> shot through the whole program, like cancer.  ...
>... [snipped]
> So they fear the spectre of having to maintain parallel files for
> a huge number of units, and getting their logic out of synch.
> ... [snipped]
> This is greatly reduced by using Ada's strong typing and separate
> compilation capabilities.  Once you've set up a fairly small
> platform interface, all the rest of the source code is invariant.
> But it takes a bit of experience to really believe that.
> ... [snipped]
> Again, Ada largely takes care of this concern.  If you missed an
> element that you need in one of your platform-specific files, the
> program won't compile.  It's actually easier to maintain most
> cross-platform dependencies in Ada, once you adapt your design to
> the Ada mindset.
> 
Thanks for the enlightening explanation above.  I have not done any
cross-platform coding in C or Ada but have often wondered how one would
do the equivalent of the C preprocessor stuff in Ada.

I have ported bought-in 3rd party libraries written in C to my platform
(e.g. a TCP/IP library for an embedded platform).  You are correct in
saying that the cross-platform stuff (e.g. size of a variable) is shot
through the whole program and it makes reading the code quite
difficult.  In the libraries I bought it was quite a nightmare till,
after staring at the code for a couple of weeks, I started to understand
all the dependencies.

Would it be possible to give an Ada example of how you would do what you
have suggested in your message above  ? i.e. what kind of things does
one put into the platform specific packages, does one not land up with
having to maintain many such packages versus just 1 file in the C case
etc ?    Some code that highlights your explanation will help.

Thanks
Rakesh