Re: [boost] [fusion][containers]reason for not reusing mpl::vector to specify element types

From: Joel de Guzman (joel_at_[hidden])
Date: 2006-09-25 18:30:31

Larry Evans wrote:
> Both fusion list and vector specify argument types with:
> 
>      template <
>          BOOST_PP_ENUM_PARAMS_WITH_A_DEFAULT(
>              FUSION_MAX_LIST_SIZE, typename T, void_)
>      >
>      struct container_whatever;
> 
> where container_whatever may be either vector or list.
> 
> What's the reason for not using mpl::vector instead of
> using yet another BOOST_PP_ENUM* call and requiring
> another *_MAX_*_SIZE macro?

I can list two:

1) Preference. It has always been my preferred interface because it
    involves less typing for the user and the result looks better.
    Consider this:

        vector<int, short, char>

    versus this:

        vector<mpl::vector<int, short, char> >

    The second is redundant and involves unnecessary interface clutter.

2) Familiarity and existing practice:

    boost::tuple<int, short, char>
    boost::variant<int, short, char>
    boost::mpl::vector<int, short, char>

    I'd find it very odd if Fusion deviates from this.
    I consider Fusion a continuation of MPL and I try my best
    to follow its interface.

Regards,
-- 
Joel de Guzman
http://www.boost-consulting.com
http://spirit.sf.net