[Boost-bugs] [Boost C++ Libraries] #10027: Allow template parameters with types rather than hardcode typename in BOOST_FUSION_DEFINE_TPL_STRUCT_INLINE (and friends)

Subject: [Boost-bugs] [Boost C++ Libraries] #10027: Allow template parameters with types rather than hardcode typename in BOOST_FUSION_DEFINE_TPL_STRUCT_INLINE (and friends)
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2014-05-08 23:40:27

#10027: Allow template parameters with types rather than hardcode typename in
BOOST_FUSION_DEFINE_TPL_STRUCT_INLINE (and friends)
--------------------------------------+---------------------
 Reporter:  Jonas Lippuner <jonas@…>  |      Owner:  djowel
     Type:  Feature Requests          |     Status:  new
Milestone:  To Be Determined          |  Component:  fusion
  Version:  Boost 1.55.0              |   Severity:  Problem
 Keywords:                            |
--------------------------------------+---------------------
 Right now, the macro `BOOST_FUSION_DEFINE_TPL_STRUCT_INLINE` creates

 {{{
 template<typename A, typename B>
 struct MyStruct { ... };
 }}}

 from

 {{{
 BOOST_FUSION_DEFINE_TPL_STRUCT_INLINE(
   (A)(B),
   MyStruct,
   (A, foo)
   (B, bar)
 )
 }}}

 But I want to put the class `template<int DIM> class Vector` into a Boost
 Fusion Struct. So the struct should allow template parameters that are not
 typenames. I would like to be able to write the following:

 {{{
 BOOST_FUSION_DEFINE_TPL_STRUCT_INLINE(
   (int DIM)(typename B),
   MyStruct,
   (Vector<DIM>, foo)
   (B, bar)
 )

 // the above becomes
 // template<int DIM, typename B>
 // struct MyStruct { ... };

 MyStruct<3, double> struct;
 }}}

 This does not currently work. The following is a working (but cumbersome)
 workaround (using C++11):

 {{{
 BOOST_FUSION_DEFINE_TPL_STRUCT_INLINE(
   (DIM)(B),
   MyStructImpl,
   (Vector<DIM::value>, foo)
   (B, bar)
 )

 template<int DIM>
 using MyStruct = MyStructImpl<boost::mpl::int_<DIM>>;

 MyStruct<3, double> struct;
 }}}

 Maybe for backwards compatibility my proposed version of
 `BOOST_FUSION_DEFINE_TPL_STRUCT_INLINE` where template parameters are
 declared as `(int DIM)(typename B)` should be named
 `BOOST_FUSION_DEFINE_FLEXIBLE_TPL_STRUCT_INLINE`.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/10027>
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