[boost] Re: Formal Review: Typeof [repost]

From: David Abrahams (dave_at_[hidden])
Date: 2005-05-21 18:37:57

"Arkadiy Vertleyb" <vertleyb_at_[hidden]> writes:

> "David Abrahams" <dave_at_[hidden]> wrote
>
>> Naw... anything of the form
>>
>>        metafunction1< metafunction2< ... >::type >::type
>>
>> can be collapsed into
>>
>>        metafunction3< ... >::type
>>
>> where
>>
>>       template <class T>
>>       struct metafunction3
>>         : metafunction1< typename metafunction2< T >::type >
>>       {};
>>
>> So there should be no need for any _TPL suffixes.
>
> Please note however, that we do not strictly operate with
> metafunctions.  The argument of TYPEOF can't be passed to a
> metafunction, which does change the rules.

I don't understand.  You can't write

template <class T>
struct decode_type_begin
  : boost::type_of::decode_type<
        typename boost::mpl::begin<T>::type
    >
{};

#define BOOST_TYPEOF(Expr)                                                      \
    boost::type_of::decode_type_begin<                                          \
        BOOST_TYPEOF_VECTOR(BOOST_TYPEOF_LIMIT_SIZE)<                           \
            BOOST_PP_ENUM(BOOST_TYPEOF_LIMIT_SIZE, BOOST_TYPEOF_TYPEITEM, Expr) \
        >                                                                       \
    >::type

??
-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com