Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!wuarchive!uunet!tcs!nujoizey!gwu
From: gwu@nujoizey.Berkeley.EDU (George Wu)
Newsgroups: comp.lang.c++
Subject: Re: precompiling header files
Message-ID: <959@tcs.tcs.com>
Date: 14 Aug 90 19:28:28 GMT
References: <617@dlogics.COM>
Sender: usenet@tcs.com
Reply-To: gwu@nujoizey.Berkeley.EDU (George Wu)
Lines: 42

In article <617@dlogics.COM>, jmd@dlogics.COM (Jens M. Dill) writes:
|> In article <946@tcs.tcs.com>, gwu@nujoizey.tcs.com (George Wu) writes:
|> > In article <9008080109.AA03748@lem>, tmb@AI.MIT.EDU (Thomas M.
Breuel) writes:
|> > |> Currently, if you want a function to be compiled but do not want its
|> > |> source code included into every compilation unit that uses it, you must
|> > |> put a declaration into a header file, and repeat the declaration (as
|> > |> part of the definition) in the implementation part.  This redundancy is
|> > |> a source of static errors and requires quite a bit of effort keeping
|> > |> two separate files (or parts of a file) consistent.
|> > 
|> >      What's wrong with including the header file in the implementation
|> > source as well?  Then the compiler will see any inconsistency between
|> > the header and the implementation.
|> 
|> What's "wrong" is that what appears in the header file must be a
DECLARATION,
|> but what appears in the source file must be a DEFINITION.

     I was aware of the difference.  You can also have the declaration in
the source file.

|> You still have to
|> maintain two independent copies of the same information (type,
storage class,
|> prototype, etc.)  An explicit or implicit EXPORT facility that collected
|> declaration information by reading the external definitions in a source file
|> would be a big convenience.

     There may be two copies of the interface definition, but the compiler
will automatically check them for consistency.  I'm not arguing the
"philisophical" merits of an export facility.  I am stating that given what
features we do have, I do not find such maintenance activity to be of almost
no effort, certainly not when compared to the task of converting all the
consumers of a library to something that has just changed its interface.

							George

----
George J Wu                           | gwu@tcs.com or ucbcad!tcs!gwu
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