Re: [boost] Re: Formal Review: Template Metaprogramming Library (MPL)

From: David Abrahams (david.abrahams_at_[hidden])
Date: 2002-07-19 06:27:16

----- Original Message -----
From: "Gennadiy Rozental" <rogeeff_at_[hidden]>

> Page 6 1.3    : It seems that all_permutation could be implemented
shorter,
> something like this (not tested!)
>
> // return an array of the N! permutations of x
> template< typename T >
> wrapper< typename permutation_holder<T>::type >
> all_permutations(T const& in)
> {
>     wrapper<typename permutation_holder<T>::type> result;
>
>     unsigned const N              = sizeof(T) / sizeof(**result.x);
>     unsigned const result_size = sizeof(result.x) / sizeof(T);
>     T*                   src            = &in; // (or &&*in?)
>
>     for( T* dst = result.x; dst != result.x + result_size; ++dst )
>     {
>         std::copy(*src, *src + N, *dst);
>         std::next_permutation(*dst, *dst + N);
>         src = dst;
>     }
>     return result;
> }

Shortness wasn't the goal there. Furthermore, shortening by replacing
comments with untested code seemed ill-advised to me at the time <wink>.

-Dave