RE: [boost] Re: new initialization lib, any interest?

From: Aleksey Gurtovoy (agurtovoy_at_[hidden])
Date: 2002-10-08 17:04:00

Yitzhak Sapir wrote:
> But learning mpl was a nice challenge so instead, I created 
> something that
> works as follows:
>   std::list<int> l3(
>     ct_init_iterator<boost::mpl::list_c<int, 2, 3, 5, 7>, 
> int>::type(),
>     ct_init_iterator<boost::mpl::list_c<int>, int>::type()
>   );
>   std::list<int> l4(
>     ct_init_iterator<boost::mpl::vector_c<int, 2, 3, 5, 7, 
> 11, 13> >::type(),
>     ct_init_iterator<boost::mpl::vector_c<int> >::type()
>   );
> 
> It's quite annoying that I don't have the equivalent of 
> Cont::value_type for list_c/vector_c/range_c.  I needed it in 
> the case of the empty list too so I'd know what kind of end-marker 
> iterator to generate. 

An oversight indeed. I'll add 'value_type' typedef to these three.

>  Also why does list_c allow specifying a type but defaults all 
> parameters to long?
> Couldn't list_c<class T, T c1, T c2, etc.> have been used?  (Like in
> integral_c?)  

Nope, because due to its variadic interface 'list_c<T,...>' needs to reserve
some single value for denoting unused arguments, and taking that value out
of range of possible values of type 'T' is not really a feasible option
(consider, for instance, T == bool).

[...]

> Also, there's a little bug in the at.hpp documentation.  The 
> documentation suggests that the format is at<N, Sequence> 
> whereas the format seems to be at<Sequence, N>.

Oh, yeah, I changed the order of parameters to comply with the review
comments, but haven't updated the docs yet. Thanks for reporting it!

> And for the pair optimization, I need a "is_pair".  That 
> would have been nice to have in type traits.
> 

    template< typename T >
    struct is_pair
        : mpl::logical_and<
              has_first<T>
            , has_second<T>
            >
    {
    };

 ;)

Thanks for the feedback!
Aleksey