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Subject: Re: [boost] [modularization] spirtit -> serialization
From: Andrey Semashev (andrey.semashev_at_[hidden])
Date: 2014-06-15 08:37:01

On Sunday 15 June 2014 15:13:55 Peter Dimov wrote:
> John Maddock wrote:
> > IMO we need a better way of looking at dependencies, perhaps by marking up
> > glue headers as optional.
> This approach causes difficulties down the road.
> module X
> X.hpp
> module Y
> Y1.hpp
> Y2.hpp (optional) includes X.hpp
> module Z
> Z.hpp includes Y2.hpp
> Does Z depend, indirectly, on X?

Yes, how could it be otherwise.

> If your answer is yes, and it must be,
> remember that Y does not depend on X, so the secondary dependencies are no
> longer the transitive closure of the primary dependencies.

It's not the question of Y depending on X anymore. If Y is header-only, it's a
question of Y2.hpp (from Y) depending on X.hpp (from X).

If Y is not header-only, the dependencies should include all dependencies of
the compiled part. Arguably, Y2.hpp may not require the compiled part, but
that case could also be handled by a metadata flag.

> The tool can be made to figure these things out, but to do so, it will need
> to create virtual submodules, one per each optional header.
> Either that, or scrap the whole module-level dependency approach and start
> tracking individual headers.

I'm for tracking headers. Submodules just impose too much difficulties to use
them on header level. Maintaining libraries should be fun.

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