[boost] [type_erasure] Some issues

25 Feb 2013

      Hi Steven,

I recently gave a presentation about type erasure in general, and your 
library in particular, at our local C++ UG (see here 
http://prezi.com/kg6d82f-_yky/type-erasure/ or the examples at 
https://github.com/CppUGBerlin/Talks/tree/master/2013_02_19_TypeErasure 
if you are interested).
During the preparation I discovered some issues I'd like to ask you about.

First I think I discovered a bug either in your lib or in clang(with 
libc++) when compiling one of the documentation examples in C++11 mode.

#include <boost/type_erasure/any.hpp>
#include <boost/type_erasure/any_cast.hpp>
#include <boost/type_erasure/builtin.hpp>
#include <boost/type_erasure/operators.hpp>
#include <boost/type_erasure/tuple.hpp>
#include <iostream>

namespace bte = boost::type_erasure;
namespace mpl = boost::mpl;

int main() {
    typedef bte::any< mpl::vector<
          bte::copy_constructible<>,
          bte::typeid_<>,
          bte::addable<>,
          bte::ostreamable<>
       > > any_type;

    any_type x(10);
    any_type y(7);
    any_type z(x + y);
    std::cout << z << std::endl;
}

Compiling this in C++03 mode is fine, in C++11 mode it fails with this 
error:

In file included from te_multi03.cpp:5:
../../Staging/type_erasure/boost/type_erasure/operators.hpp:187:1: 
error: no matching function for call to 'call' 
BOOST_TYPE_ERASURE_BINARY_OPERATOR(addable, +)
see [1] below for full error.

The next are some things which I didn't get to work, and the 
documentation is silent on any pitfalls.

I tried to implement Sean Parent's example from his Value Semantics talk 
and failed to write a concept that calls free functions instead of 
members. Here is what I tried (full code and error at [2] below):

template<class OBJ, class T>
struct drawable {
    static void apply(const OBJ& obj, T& os, size_t pos) {
       draw(obj, os, pos);
    }
};

I get an error like: error call to function 'draw' that is neither 
visible in the template definition nor found by argument-dependent lookup

I worked around this problem by defining a concept map, but that is not 
realy a good solution.

On researching a better solution I saw that you already added the 
convenience macros BOOST_TYPE_ERASURE_MEMBER and 
BOOST_TYPE_ERASURE_FREE, but didn't have much luck with them.
Is there a compileable example where they are used somewhere?

Best regards

Fabio

**** [1] ***************************************************************
[1] full error docu example:

In file included from te_multi03.cpp:5:
../../Staging/type_erasure/boost/type_erasure/operators.hpp:187:1: 
error: no matching function for call to 'call'
BOOST_TYPE_ERASURE_BINARY_OPERATOR(addable, +)
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../../Staging/type_erasure/boost/type_erasure/operators.hpp:166:20: 
note: expanded from macro 'BOOST_TYPE_ERASURE_BINARY_OPERATOR'
             return ::boost::type_erasure::call(name<T, U, R>(), lhs, 
rhs);  \
                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~
te_multi03.cpp:25:17: note: in instantiation of member function 
'boost::type_erasure::operator+' requested here
    any_type z(x + y);
                 ^
../../Staging/type_erasure/boost/type_erasure/call.hpp:323:1: note: 
candidate template ignored: failed template argument deduction
call(
^
../../Staging/type_erasure/boost/type_erasure/call.hpp:356:1: note: 
candidate template ignored: substitution failure [with Op = 
boost::type_erasure::addable<boost::type_erasure::_self, 
boost::type_erasure::_self,
       boost::type_erasure::_self>, U = <const 
boost::type_erasure::any<boost::mpl::vector<boost::type_erasure::copy_constructible<boost::type_erasure::_self>, 
boost::type_erasure::typeid_<boost::type_erasure::_self>,
       boost::type_erasure::addable<boost::type_erasure::_self, 
boost::type_erasure::_self, boost::type_erasure::_self>, 
boost::type_erasure::ostreamable<std::__1::basic_ostream<char>, 
boost::type_erasure::_self>, mpl_::na, mpl_::na,
       mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, 
mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, 
mpl_::na>, boost::type_erasure::_self>,

boost::type_erasure::param<boost::mpl::vector<boost::type_erasure::copy_constructible<boost::type_erasure::_self>, 
boost::type_erasure::typeid_<boost::type_erasure::_self>, 
boost::type_erasure::addable<boost::type_erasure::_self,
       boost::type_erasure::_self, boost::type_erasure::_self>, 
boost::type_erasure::ostreamable<std::__1::basic_ostream<char>, 
boost::type_erasure::_self>, mpl_::na, mpl_::na, mpl_::na, mpl_::na, 
mpl_::na, mpl_::na, mpl_::na, mpl_::na,
       mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, 
mpl_::na, mpl_::na>, const boost::type_erasure::_self &>>]: no type 
named 'type' in

'boost::type_erasure::detail::call_result<boost::type_erasure::addable<boost::type_erasure::_self, 
boost::type_erasure::_self, boost::type_erasure::_self>, void (const

boost::type_erasure::any<boost::mpl::vector<boost::type_erasure::copy_constructible<boost::type_erasure::_self>, 
boost::type_erasure::typeid_<boost::type_erasure::_self>, 
boost::type_erasure::addable<boost::type_erasure::_self,
       boost::type_erasure::_self, boost::type_erasure::_self>, 
boost::type_erasure::ostreamable<std::__1::basic_ostream<char>, 
boost::type_erasure::_self>, mpl_::na, mpl_::na, mpl_::na, mpl_::na, 
mpl_::na, mpl_::na, mpl_::na, mpl_::na,
       mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, 
mpl_::na, mpl_::na>, boost::type_erasure::_self> &, 
boost::type_erasure::param<boost::mpl::vector<boost::type_erasure::copy_constructible<boost::type_erasure::_self>,
       boost::type_erasure::typeid_<boost::type_erasure::_self>, 
boost::type_erasure::addable<boost::type_erasure::_self, 
boost::type_erasure::_self, boost::type_erasure::_self>,
       boost::type_erasure::ostreamable<std::__1::basic_ostream<char>, 
boost::type_erasure::_self>, mpl_::na, mpl_::na, mpl_::na, mpl_::na, 
mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, 
mpl_::na, mpl_::na, mpl_::na,
       mpl_::na, mpl_::na>, const boost::type_erasure::_self &> &), void>'
call(
^
1 error generated.

**** [2] ***************************************************************
[2] Code and error for Value semantic example:

#include <boost/type_erasure/any.hpp>
#include <boost/type_erasure/concept_interface.hpp>
#include <boost/type_erasure/rebind_any.hpp>
#include <boost/type_erasure/free.hpp>
#include <vector>

namespace bte = boost::type_erasure;
namespace mpl = boost::mpl;

//--------------------------------------------------------------------------------------------------

template<class OBJ, class T>
struct drawable {
    static void apply(const OBJ& obj, T& os, size_t pos) { draw(obj, os, 
pos); }
};

namespace boost { namespace type_erasure {
    template<class OBJ, class T, class Base>
    struct concept_interface< ::drawable<OBJ, T>, Base, OBJ> : Base {
       void draw(typename rebind_any<Base, T&>::type os, size_t pos) const {
          call(::drawable<OBJ, T>(), *this, os, pos);
       }
    };
} }

using object_t = bte::any< mpl::vector<
                               bte::copy_constructible<>,
                               drawable<bte::_self, std::ostream>
                  >>;

//--------------------------------------------------------------------------------------------------

void draw(const int& value, std::ostream& out, size_t position) {
    out << std::string(position, ' ') << "int = " << value << std::endl;
}

void draw(const std::string& value, std::ostream& out, size_t position) {
    out << std::string(position, ' ') << "string = " << value << std::endl;
}

struct my_class_t {};
void draw(const my_class_t&, std::ostream& out, size_t position) {
    out << std::string(position, ' ') << "my_class_t" << std::endl;
}

//--------------------------------------------------------------------------------------------------

using document_t = std::vector<object_t>;  // or 
std::vector<copy_on_write<object_t>>;

void draw(const document_t& x, std::ostream& out, size_t position) {
    out << std::string(position, ' ') << "<document>" << std::endl;
    for (auto& e : x) {
       e.draw(out, position + 2);
    }
    out << std::string(position, ' ') << "</document>" << std::endl;
}

//--------------------------------------------------------------------------------------------------

using history_t = std::vector<document_t>;

void commit(history_t& x) { assert(x.size()); x.push_back(x.back()); }
void undo(history_t& x) { assert(x.size()); x.pop_back(); }
document_t& current(history_t& x) { assert(x.size()); return x.back(); }

//--------------------------------------------------------------------------------------------------

int main () {

    history_t h(1);
    current(h).emplace_back(0);
    current(h).emplace_back(std::string("Hello!"));

    draw(current(h), std::cout, 0);
    std::cout << "--------------------------" << std::endl;

    commit(h);

    current(h).emplace_back(current(h));
    current(h).emplace_back(my_class_t());

    draw(current(h), std::cout, 0);
    std::cout << "--------------------------" << std::endl;

    undo(h);
    draw(current(h), std::cout, 0);
}

**** Error: ************************************************************

te_sp_copy.cpp:14:59: error: call to function 'draw' that is neither 
visible in the template definition nor found by argument-dependent lookup
    static void apply(const OBJ& obj, T& os, size_t pos) { draw(obj, os, 
pos); }
                                                           ^
../../Staging/type_erasure/boost/type_erasure/detail/instantiate.hpp:91:28: 
note: in instantiation of member function 'drawable<int, 
std::__1::basic_ostream<char> >::apply' requested here
         BOOST_PP_REPEAT(N, BOOST_TYPE_ERASURE_INSTANTIATE_IMPL, 
concept_sequence)
                            ^
/usr/local/include/boost/preprocessor/repetition/repeat.hpp:38:60: note: 
expanded from macro 'BOOST_PP_REPEAT_1'
# define BOOST_PP_REPEAT_1(c, m, d) BOOST_PP_REPEAT_1_I(c, m, d)
                                                            ^
/usr/local/include/boost/preprocessor/repetition/repeat.hpp:43:63: note: 
expanded from macro 'BOOST_PP_REPEAT_1_I'
# define BOOST_PP_REPEAT_1_I(c, m, d) BOOST_PP_REPEAT_1_ ## c(m, d)
                                                               ^
/usr/local/include/boost/preprocessor/repetition/repeat.hpp:54:62: note: 
expanded from macro 'BOOST_PP_REPEAT_1_3'
# define BOOST_PP_REPEAT_1_3(m, d) BOOST_PP_REPEAT_1_2(m, d) m(2, 2, d)
                                                              ^
../../Staging/type_erasure/boost/type_erasure/detail/instantiate.hpp:70:47: 
note: expanded from macro 'BOOST_TYPE_ERASURE_INSTANTIATE_IMPL'
     (void)&::boost::mpl::at_c<data, n>::type::apply;
                                               ^
../../Staging/type_erasure/boost/type_erasure/any.hpp:182:13: note: in 
instantiation of function template specialization

'boost::type_erasure::detail::instantiate_concept3::apply<boost::mpl::vector<boost::type_erasure::copy_constructible<boost::type_erasure::_self>, 
drawable<boost::type_erasure::_self, std::__1::basic_ostream<char> >, 
mpl_::na,
       mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, 
mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, 
mpl_::na, mpl_::na, mpl_::na, mpl_::na>, 
boost::mpl::map1<boost::mpl::pair<boost::type_erasure::_self,
       int> > >' requested here
             BOOST_TYPE_ERASURE_INSTANTIATE1(Concept, T, U),
             ^
../../Staging/type_erasure/boost/type_erasure/detail/instantiate.hpp:51:14: 
note: expanded from macro 'BOOST_TYPE_ERASURE_INSTANTIATE1'
     >::type::apply(                                             \
              ^
/usr/bin/../lib/c++/v1/memory:1681:31: note: in instantiation of 
function template specialization 
'boost::type_erasure::any<boost::mpl::vector<boost::type_erasure::copy_constructible<boost::type_erasure::_self>,
       drawable<boost::type_erasure::_self, 
std::__1::basic_ostream<char> >, mpl_::na, mpl_::na, mpl_::na, mpl_::na, 
mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, 
mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na,
       mpl_::na, mpl_::na>, boost::type_erasure::_self>::any<int>' 
requested here
             ::new((void*)__p) _Up(_VSTD::forward<_Args>(__args)...);
                               ^
/usr/bin/../lib/c++/v1/memory:1608:18: note: in instantiation of 
function template specialization 
'std::__1::allocator<boost::type_erasure::any<boost::mpl::vector<boost::type_erasure::copy_constructible<boost::type_erasure::_self>,
       drawable<boost::type_erasure::_self, 
std::__1::basic_ostream<char> >, mpl_::na, mpl_::na, mpl_::na, mpl_::na, 
mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, 
mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na,
       mpl_::na, mpl_::na>, boost::type_erasure::_self>
...
::construct<boost::type_erasure::any<boost::mpl::vector<boost::type_erasure::copy_constructible<boost::type_erasure::_self>, drawable<boost::type_erasure::_self,
       std::__1::basic_ostream<char> >, mpl_::na, mpl_::na, mpl_::na, 
mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, 
mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, 
mpl_::na>,
       boost::type_erasure::_self>, int>' requested here
             {__a.construct(__p, _VSTD::forward<_Args>(__args)...);}
                  ^
/usr/bin/../lib/c++/v1/memory:1492:14: note: in instantiation of 
function template specialization
'std::__1::allocator_traits<std::__1::allocator<boost::type_erasure::any<boost::mpl::vector<boost::type_erasure::copy_constructible<boost::type_erasure::_self>, 
drawable<boost::type_erasure::_self, std::__1::basic_ostream<char> >,
       mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, 
mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, 
mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na>, 
boost::type_erasure::_self> >
...
::__construct<boost::type_erasure::any<boost::mpl::vector<boost::type_erasure::copy_constructible<boost::type_erasure::_self>, drawable<boost::type_erasure::_self, std::__1::basic_ostream<char> >, mpl_::na, mpl_::na, mpl_::na,
       mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, 
mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, 
mpl_::na, mpl_::na>, boost::type_erasure::_self>, int>' requested here
             {__construct(__has_construct<allocator_type, pointer, 
_Args...>(),
              ^
/usr/bin/../lib/c++/v1/vector:1519:25: note: in instantiation of 
function template specialization
...
::construct<boost::type_erasure::any<boost::mpl::vector<boost::type_erasure::copy_constructible<boost::type_erasure::_self>, drawable<boost::type_erasure::_self, std::__1::basic_ostream<char> >, mpl_::na, mpl_::na, mpl_::na,
       mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, 
mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, 
mpl_::na, mpl_::na>, boost::type_erasure::_self>, int>' requested here
         __alloc_traits::construct(this->__alloc(),
                         ^
te_sp_copy.cpp:71:15: note: in instantiation of function template 
specialization 
'std::__1::vector<boost::type_erasure::any<boost::mpl::vector<boost::type_erasure::copy_constructible<boost::type_erasure::_self>,
       drawable<boost::type_erasure::_self, 
std::__1::basic_ostream<char> >, mpl_::na, mpl_::na, mpl_::na, mpl_::na, 
mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, 
mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na,
       mpl_::na, mpl_::na>, boost::type_erasure::_self>, 
std::__1::allocator<boost::type_erasure::any<boost::mpl::vector<boost::type_erasure::copy_constructible<boost::type_erasure::_self>, 
drawable<boost::type_erasure::_self,
       std::__1::basic_ostream<char> >, mpl_::na, mpl_::na, mpl_::na, 
mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, 
mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, 
mpl_::na>,
       boost::type_erasure::_self> > >::emplace_back<int>' requested here
    current(h).emplace_back(0);
               ^
te_sp_copy.cpp:33:6: note: 'draw' should be declared prior to the call site
void draw(const int& value, std::ostream& out, size_t position) {
      ^
te_sp_copy.cpp:14:59: error: call to function 'draw' that is neither 
visible in the template definition nor found by argument-dependent lookup
    static void apply(const OBJ& obj, T& os, size_t pos) { draw(obj, os,
'std::__1::allocator_traits<std::__1::allocator<boost::type_erasure::any<boost::mpl::vector<boost::type_erasure::copy_constructible<boost::type_erasure::_self>, 
drawable<boost::type_erasure::_self, std::__1::basic_ostream<char> >,
       mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, 
mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, 
mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na>, 
boost::type_erasure::_self> >

pos); }
                                                           ^
../../Staging/type_erasure/boost/type_erasure/detail/instantiate.hpp:91:28: 
note: in instantiation of member function 
'drawable<std::__1::basic_string<char>, std::__1::basic_ostream<char>
...
::apply' requested here
         BOOST_PP_REPEAT(N, BOOST_TYPE_ERASURE_INSTANTIATE_IMPL, 
concept_sequence)
                            ^
/usr/local/include/boost/preprocessor/repetition/repeat.hpp:38:60: note: 
expanded from macro 'BOOST_PP_REPEAT_1'
# define BOOST_PP_REPEAT_1(c, m, d) BOOST_PP_REPEAT_1_I(c, m, d)
                                                            ^
/usr/local/include/boost/preprocessor/repetition/repeat.hpp:43:63: note: 
expanded from macro 'BOOST_PP_REPEAT_1_I'
# define BOOST_PP_REPEAT_1_I(c, m, d) BOOST_PP_REPEAT_1_ ## c(m, d)
                                                               ^
/usr/local/include/boost/preprocessor/repetition/repeat.hpp:54:62: note: 
expanded from macro 'BOOST_PP_REPEAT_1_3'
# define BOOST_PP_REPEAT_1_3(m, d) BOOST_PP_REPEAT_1_2(m, d) m(2, 2, d)
                                                              ^
../../Staging/type_erasure/boost/type_erasure/detail/instantiate.hpp:70:47: 
note: expanded from macro 'BOOST_TYPE_ERASURE_INSTANTIATE_IMPL'
     (void)&::boost::mpl::at_c<data, n>::type::apply;
                                               ^
../../Staging/type_erasure/boost/type_erasure/any.hpp:182:13: note: in 
instantiation of function template specialization
'boost::type_erasure::detail::instantiate_concept3::apply<boost::mpl::vector<boost::type_erasure::copy_constructible<boost::type_erasure::_self>, 
drawable<boost::type_erasure::_self, std::__1::basic_ostream<char> >, 
mpl_::na,
       mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, 
mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, 
mpl_::na, mpl_::na, mpl_::na, mpl_::na>, 
boost::mpl::map1<boost::mpl::pair<boost::type_erasure::_self,
       std::__1::basic_string<char> > > >' requested here
             BOOST_TYPE_ERASURE_INSTANTIATE1(Concept, T, U),
             ^
../../Staging/type_erasure/boost/type_erasure/detail/instantiate.hpp:51:14: 
note: expanded from macro 'BOOST_TYPE_ERASURE_INSTANTIATE1'
     >::type::apply(                                             \
              ^
/usr/bin/../lib/c++/v1/memory:1681:31: note: in instantiation of 
function template specialization 
'boost::type_erasure::any<boost::mpl::vector<boost::type_erasure::copy_constructible<boost::type_erasure::_self>,
       drawable<boost::type_erasure::_self, 
std::__1::basic_ostream<char> >, mpl_::na, mpl_::na, mpl_::na, mpl_::na, 
mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, 
mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na,
       mpl_::na, mpl_::na>, 
boost::type_erasure::_self>::any<std::__1::basic_string<char> >' 
requested here
             ::new((void*)__p) _Up(_VSTD::forward<_Args>(__args)...);
                               ^
/usr/bin/../lib/c++/v1/memory:1608:18: note: in instantiation of 
function template specialization 
'std::__1::allocator<boost::type_erasure::any<boost::mpl::vector<boost::type_erasure::copy_constructible<boost::type_erasure::_self>,
       drawable<boost::type_erasure::_self, 
std::__1::basic_ostream<char> >, mpl_::na, mpl_::na, mpl_::na, mpl_::na, 
mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, 
mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na,
       mpl_::na, mpl_::na>, boost::type_erasure::_self>
...
::construct<boost::type_erasure::any<boost::mpl::vector<boost::type_erasure::copy_constructible<boost::type_erasure::_self>, drawable<boost::type_erasure::_self,
       std::__1::basic_ostream<char> >, mpl_::na, mpl_::na, mpl_::na, 
mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, 
mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, 
mpl_::na>,
       boost::type_erasure::_self>, std::__1::basic_string<char> >' 
requested here
             {__a.construct(__p, _VSTD::forward<_Args>(__args)...);}
                  ^
/usr/bin/../lib/c++/v1/memory:1492:14: note: in instantiation of 
function template specialization
'std::__1::allocator_traits<std::__1::allocator<boost::type_erasure::any<boost::mpl::vector<boost::type_erasure::copy_constructible<boost::type_erasure::_self>, 
drawable<boost::type_erasure::_self, std::__1::basic_ostream<char> >,
       mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, 
mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, 
mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na>, 
boost::type_erasure::_self> >
...
::__construct<boost::type_erasure::any<boost::mpl::vector<boost::type_erasure::copy_constructible<boost::type_erasure::_self>, drawable<boost::type_erasure::_self, std::__1::basic_ostream<char> >, mpl_::na, mpl_::na, mpl_::na,
       mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, 
mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, 
mpl_::na, mpl_::na>, boost::type_erasure::_self>, 
std::__1::basic_string<char> >' requested here
             {__construct(__has_construct<allocator_type, pointer, 
_Args...>(),
              ^
/usr/bin/../lib/c++/v1/vector:1519:25: note: in instantiation of 
function template specialization
'std::__1::allocator_traits<std::__1::allocator<boost::type_erasure::any<boost::mpl::vector<boost::type_erasure::copy_constructible<boost::type_erasure::_self>, 
drawable<boost::type_erasure::_self, std::__1::basic_ostream<char> >,
       mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, 
mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, 
mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na>, 
boost::type_erasure::_self> >
...
::construct<boost::type_erasure::any<boost::mpl::vector<boost::type_erasure::copy_constructible<boost::type_erasure::_self>, drawable<boost::type_erasure::_self, std::__1::basic_ostream<char> >, mpl_::na, mpl_::na, mpl_::na,
       mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, 
mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, 
mpl_::na, mpl_::na>, boost::type_erasure::_self>, 
std::__1::basic_string<char> >' requested here
         __alloc_traits::construct(this->__alloc(),
                         ^
te_sp_copy.cpp:72:15: note: in instantiation of function template 
specialization 
'std::__1::vector<boost::type_erasure::any<boost::mpl::vector<boost::type_erasure::copy_constructible<boost::type_erasure::_self>,
       drawable<boost::type_erasure::_self, 
std::__1::basic_ostream<char> >, mpl_::na, mpl_::na, mpl_::na, mpl_::na, 
mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, 
mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na,
       mpl_::na, mpl_::na>, boost::type_erasure::_self>, 
std::__1::allocator<boost::type_erasure::any<boost::mpl::vector<boost::type_erasure::copy_constructible<boost::type_erasure::_self>, 
drawable<boost::type_erasure::_self,
       std::__1::basic_ostream<char> >, mpl_::na, mpl_::na, mpl_::na, 
mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, 
mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, 
mpl_::na>,
       boost::type_erasure::_self> > 
::emplace_back<std::__1::basic_string<char> >' requested here
    current(h).emplace_back(std::string("Hello!"));
               ^
te_sp_copy.cpp:37:6: note: 'draw' should be declared prior to the call site
void draw(const std::string& value, std::ostream& out, size_t position) {
      ^
2 errors generated.

[boost] [type_erasure] Some issues

Fabio Fracassi