Re: [boost] [type_traits] Modularization proposal

Subject: Re: [boost] [type_traits] Modularization proposal
From: Vicente J. Botet Escriba (vicente.botet_at_[hidden])
Date: 2014-09-17 07:21:16

Le 16/09/14 21:47, Andrey Semashev a écrit :
> On Tuesday 16 September 2014 20:06:27 John Maddock wrote:
>>> Boost.TypeTraits is used in lots of other Boost libraries, and it
>>> currently
>>> unnecessarily pulls MPL and TypeOf. The dependencies are introduced by
>>> just
>>> these two public headers: floating_point_promotion.hpp and
>>> common_type.hpp.
>>> I'd like to avoid these dependencies.
>>>
>>> I propose to extract common_type.hpp (and its implementation and tests)
>>> into a sublib within type_traits (e.g. type_traits/common_type).
>>>
>>> As for floating_point_promotion.hpp, it is used in promote.hpp, which is
>>> using integral_promotion.hpp. I can see two ways of tackling it:
>>>
>>> 1. Extract all promotion traits into a sublib (e.g.
>>> type_traits/promotion).
>>> This includes floating_point_promotion.hpp, integral_promotion.hpp and
>>> promote.hpp, as well as their tests.
>> What happens to boost/type_traits.hpp in this scheme (which depends on
>> *all* of type_traits)?
> Hmm, I didn't notice that header. Ok, assuming we don't want to move this one
> header to its own sublib, what if we approach it from the other side. We can
> move all type traits except common_type.hpp and type_traits.hpp to a sublib
> base (i.e. type_traits/base). floating_point_promotion.hpp would be changed to
> not depend on MPL before moving to base.
>
This will work. However, currently the submodules depend on the module, 
not the opposite. I don't know if this is perturbing.
So, here is another alternative. Let everything in place except 
type_traits.hpp type_traits/common_type.hpp, which are move to two 
sub-modules TypeTraits.All and TypeTraits.CommonType with the following 
dependencies

TypeTraits.All -> TypeTraits TypeTraits.CommonType
TypeTraits.CommonType -> TypeTraits TypeOf
TypeOf -> TypeTraits

Vicente