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Subject: Re: [boost] [modularization] proposal and poll
From: Julian Gonggrijp (j.gonggrijp_at_[hidden])
Date: 2014-05-30 01:20:27

Glen Fernandes wrote:

> On Thu, May 29, 2014 at 1:22 PM, Julian Gonggrijp wrote:
>> - Manually: this is cumbersome and generally hard because there are
>> many (undocumented) interdependencies between Boost libraries.
>> - Automatically: as far as I know Ryppl is the only existing attempt
>> at providing automated dependency handling for Boost, but it is a
>> very ambitious project that attempts to do much more and it is
>> currently neither finished nor being actively developed.
>> I think there could be a less ambitious but faster way to provide
>> automated dependency handling. It would take no more than some static
>> configuration, to list for each library what other Boost libraries it
>> depends on, combined with a simple script that automatically traverses
>> the dependency graph and clones just the necessary submodules. This
>> script may then be hooked into the bootstrap script. I think I could
>> write the dependency handler, and I would be willing to, though I
>> can't currently provide any indication of when I would be able to
>> start.
> It would be nice if both approaches (static configuration, automatic
> identification) take into account - or allow you to specify -
> conditional dependencies (e.g. dependencies based on identification of
> supported or unsupported features determined by Boost.Config).

In my reply to Robert Ramey just now I mentioned the possibility to
use Boost.Bjam's <toolset> to handle this. There might be other ways
as well. Given that it is probably feasible to account for this,
would you vote in favour of what I propose?

> For example:
> Boost.Align should only be considered as depending on Boost.TypeTraits
> (for boost::alignment_of) if BOOST_NO_CXX11_HDR_TYPE_TRAITS is
> defined; otherwise it uses the C++11 standard library (for
> std::alignment_of). Similarly, it only depends on Boost.Utility (for
> boost::addressof) if BOOST_NO_CXX11_STD_ADDRESSOF is defined;
> otherwise it uses the C++11 standard library (for std::addressof).
> For anyone wanting to consume Boost.Align, should they have a
> conforming C++11 implementation, they should see Boost.Align's
> dependencies as only Boost.Config and Boost.Integer. Otherwise,
> someone consuming Boost.Align with a totally non-conforming C++11
> implementation should see its dependencies as: Boost.Config,
> Boost.Integer, Boost.Utility, Boost.TypeTraits.
> Glen

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