Re: [boost] [mpl][docs]why use list?

Subject: Re: [boost] [mpl][docs]why use list?
From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2009-03-27 11:43:43

AMDG

Larry Evans wrote:
> After viewing the code some more, I'm wondering if the memoization is
> not also possible with vectors with identical tails.  That's because,
> from:
>
>
> https://svn.boost.org/trac/boost/browser/trunk/boost/mpl/vector/aux_/preprocessed/typeof_based/vector10.hpp 
>
>
> containing:
>
>   template<
> 39          typename T0, typename T1, typename T2
> 40        >
> 41    struct vector3
> 42        : v_item<
> 43              T2
> 44            , vector2< T0,T1 >
> 45            >
> 46    {
> 47        typedef vector3 type;
> 48    };
>
> it appears that vector would have a memoization advantage for idential
> heads. For instance:
>
>   vector<T0,T1,T2_1> vs vector<T0,T1,T2_2>
>
> from the above vector3 code:
>
>   v_item<T2_1,vector2<T0,T1> > vs v_item<T2_2,vector2<T0,T1> >
>
> So, maybe list has an advantage for identical tails but vector has an
> advantage for identical heads?

No.  Take a look at how the iterators for vector work.

template<
      typename Vector
    , BOOST_MPL_AUX_NTTP_DECL(long, n_)
    >
struct v_iter;

Iterators into different vectors are always distinct.

In Christ,
Steven Watanabe