id,summary,reporter,owner,description,type,status,milestone,component,version,severity,resolution,keywords,cc
13418,Request: allow general typelist types in BOOST_AUTO_TEST_CASE_TEMPLATE(),Tony E Lewis <tonyelewis@…>,Raffi Enficiaud,"In ticket:12092 I requested that `BOOST_AUTO_TEST_CASE_TEMPLATE()` be generalised to allow users to specify the typelist as a `std::tuple` of types, as well as a `boost::mpl::vector`. You added this feature - thanks very much.

As discussed in ticket:12092#comment:7, since I made the original request, I've come to realise that TMP gurus avoid using `std::tuple` as a typelist because it has complex guts that needlessly eat up compiler-time for each instantiation. Instead, I think they typically just use an arbitrary empty template struct, eg:

{{{
#!cpp
template <typename...> struct my_typelist_wrapper {};

using a_typelist = my_typelist_wrapper<int, char>;
}}}

With this in mind, it might be nice to consider finessing the conversion to `boost::mpl::vector` so that it works from any arbitrary such typelist (including `std::tuple`). Here's an illustrative implementation of the idea (which I've slightly tweaked since ticket:12092#comment:7 so that if the metafunction is called with anything other than a single, valid typelist, it will return a dummy type with a descriptive name which will hopefully make the compiler errors more helpful):

{{{
#!cpp
struct arg_type_is_not_single_valid_typelist final {
   arg_type_is_not_single_valid_typelist() = delete;
   ~arg_type_is_not_single_valid_typelist() = delete;
   arg_type_is_not_single_valid_typelist(const arg_type_is_not_single_valid_typelist &) = delete;
   arg_type_is_not_single_valid_typelist & operator=(const arg_type_is_not_single_valid_typelist &) = delete;
};

template <typename...>
struct mpl_vector_of_typelist_impl {
   using type = arg_type_is_not_single_valid_typelist;
};

template <template <typename...> class T,
          typename... Us>
struct mpl_vector_of_typelist_impl< T< Us... > > {
   using type = boost::mpl::vector<Us...>;
};

template <typename T>
using mpl_vector_of_typelist_t = typename mpl_vector_of_typelist_impl<T>::type;
}}}


Here are some simple usage examples:

{{{
#!cpp

template <typename...> struct my_typelist_wrapper {};

static_assert(  std::is_same<  mpl_vector_of_typelist_t< my_typelist_wrapper< int, char > >,  boost::mpl::vector<int, char >         >::value, """" );
static_assert(  std::is_same<  mpl_vector_of_typelist_t< std::tuple         < int, char > >,  boost::mpl::vector<int, char >         >::value, """" );
static_assert(  std::is_same<  mpl_vector_of_typelist_t< int                              >,  arg_type_is_not_single_valid_typelist  >::value, """" );
}}}",Feature Requests,closed,Boost 1.69,test,Boost 1.66.0,Optimization,fixed,1.70 target,