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Subject: Re: [boost] Formal Review Request: TypeErasure
From: lcaminiti (lorcaminiti_at_[hidden])
Date: 2012-06-18 12:45:31

lcaminiti wrote
>
> I will use the lib in some use cases that I ran into the past and let you
> know if I find a nice example not too complex (I don't remember what the
> use cases were but they were about type erasure).
>

Why this does not compile?

#include <boost/type_erasure/any.hpp>
#include <boost/type_erasure/builtin.hpp>
#include <boost/type_erasure/operators.hpp>
#include <boost/mpl/vector.hpp>
#include <iostream>

struct display
{
    public: template< typename T >
    explicit display ( T const& obj ) : obj_(obj) {}

    public: void print ( void ) { std::cout << obj_ << std::endl; }

    private: boost::type_erasure::any<
        boost::mpl::vector<
              boost::type_erasure::copy_constructible<>
            , boost::type_erasure::typeid_<>
            , boost::type_erasure::ostreamable<>
>
> obj_;
};

int main ( void )
{
    display i(123), s("abc");
    i.print();
    s.print();
    return 0;
}

Using GCC 4.5.3 on Cygwin with Boost 1.50.0 Beta 1, I get:

In file included from ../boost/type_erasure/detail/access.hpp:14:0,
                 from ../boost/type_erasure/any.hpp:34,
                 from 01.cpp:2:
../boost/type_erasure/detail/storage.hpp: In constructor
‘boost::type_erasure::detail::storage::storage(const T&) [with T = char
[4]]’:
../boost/type_erasure/any.hpp:167:22: instantiated from
‘boost::type_erasure::any<Concept, T>::any(const U&) [with U = char [4],
Concept = boost::mpl::vector<boost::type_erasure::copy_constructible&lt;>,
boost::type_erasure::typeid_<>, boost::type_erasure::ostreamable<> >, T =
boost::type_erasure::_self]’
01.cpp:11:49: instantiated from ‘display::display(const T&) [with T =
char [4]]’
01.cpp:26:28: instantiated from here
../boost/type_erasure/detail/storage.hpp:24:44: error: ISO C++ forbids
initialization in array new
In file included from
../../../1_50_0_beta1.cygwin/boost/preprocessor/iteration/detail/iter/forward1.hpp:52:0,
                 from
../boost/type_erasure/detail/rebind_placeholders.hpp:127,
                 from ../boost/type_erasure/detail/normalize.hpp:31,
                 from ../boost/type_erasure/any.hpp:36,
                 from 01.cpp:2:
../boost/type_erasure/detail/rebind_placeholders.hpp: At global scope:
../boost/type_erasure/detail/rebind_placeholders.hpp: In instantiation of
‘boost::type_erasure::detail::rebind_placeholders_in_argument<boost::type_erasure::_self(const
boost::type_erasure::_self&amp;),
boost::mpl::map&lt;boost::mpl::pair&lt;boost::type_erasure::_self, char
[4]>, 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, mpl_::na> >’:
../boost/type_erasure/detail/rebind_placeholders.hpp:149:63: instantiated
from
‘boost::type_erasure::detail::rebind_placeholders<boost::type_erasure::constructible&lt;boost::type_erasure::_self(const
boost::type_erasure::_self&amp;)>,
boost::mpl::map<boost::mpl::pair&lt;boost::type_erasure::_self, char [4]>,
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, mpl_::na> >’
../boost/type_erasure/detail/adapt_to_vtable.hpp:53:7: instantiated from
‘boost::type_erasure::detail::rebind_placeholders<boost::type_erasure::detail::vtable_adapter&lt;boost::type_erasure::constructible&lt;boost::type_erasure::_self(const
boost::type_erasure::_self&amp;)>,
boost::type_erasure::detail::storage(const
boost::type_erasure::detail::storage&)>,
boost::mpl::map<boost::mpl::pair&lt;boost::type_erasure::_self, char [4]>,
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, mpl_::na> >’
../../../1_50_0_beta1.cygwin/boost/mpl/aux_/has_type.hpp:20:1:
instantiated from ‘const bool
boost::mpl::aux::has_type<boost::type_erasure::detail::rebind_placeholders&lt;boost::type_erasure::detail::vtable_adapter&lt;boost::type_erasure::constructible&lt;boost::type_erasure::_self(const
boost::type_erasure::_self&amp;)>,
boost::type_erasure::detail::storage(const
boost::type_erasure::detail::storage&)>,
boost::mpl::map<boost::mpl::pair&lt;boost::type_erasure::_self, char [4]>,
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, mpl_::na> >, mpl_::bool_<true>
>::value’
../../../1_50_0_beta1.cygwin/boost/mpl/aux_/has_type.hpp:20:1:
instantiated from
‘boost::mpl::aux::has_type<boost::type_erasure::detail::rebind_placeholders&lt;boost::type_erasure::detail::vtable_adapter&lt;boost::type_erasure::constructible&lt;boost::type_erasure::_self(const
boost::type_erasure::_self&amp;)>,
boost::type_erasure::detail::storage(const
boost::type_erasure::detail::storage&)>,
boost::mpl::map<boost::mpl::pair&lt;boost::type_erasure::_self, char [4]>,
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, mpl_::na> >, mpl_::bool_<true> >’
../../../1_50_0_beta1.cygwin/boost/mpl/aux_/preprocessed/gcc/quote.hpp:56:5:
instantiated from
‘boost::mpl::quote2<boost::type_erasure::detail::rebind_placeholders,
mpl_::void_>::apply<boost::type_erasure::detail::vtable_adapter&lt;boost::type_erasure::constructible&lt;boost::type_erasure::_self(const
boost::type_erasure::_self&amp;)>,
boost::type_erasure::detail::storage(const
boost::type_erasure::detail::storage&)>,
boost::mpl::map<boost::mpl::pair&lt;boost::type_erasure::_self, char [4]>,
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, mpl_::na> >’
../../../1_50_0_beta1.cygwin/boost/mpl/aux_/preprocessed/gcc/apply_wrap.hpp:49:1:
[ skipping 14 instantiation contexts ]
../../../1_50_0_beta1.cygwin/boost/mpl/transform.hpp:138:1: instantiated
from
‘boost::mpl::transform<boost::mpl::v_item&lt;boost::type_erasure::detail::vtable_adapter&lt;boost::type_erasure::ostreamable&lt;>,
void(std::basic_ostream<char>&, const
boost::type_erasure::detail::storage&)>,
boost::mpl::v_item<boost::type_erasure::typeid_&lt;>,
boost::mpl::v_item<boost::type_erasure::destructible&lt;boost::type_erasure::_self>,
boost::mpl::v_item<boost::type_erasure::detail::vtable_adapter&lt;boost::type_erasure::constructible&lt;boost::type_erasure::_self(const
boost::type_erasure::_self&amp;)>,
boost::type_erasure::detail::storage(const
boost::type_erasure::detail::storage&)>, boost::mpl::vector0<mpl_::na>, 0>,
0>, 0>, 0>,
boost::type_erasure::detail::rebind_placeholders<mpl_::arg&lt;1>,
boost::mpl::map<boost::mpl::pair&lt;boost::type_erasure::_self, char [4]>,
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, mpl_::na> >, mpl_::na, mpl_::na>’
../boost/type_erasure/binding.hpp:163:13: instantiated from
‘boost::type_erasure::binding<Concept>::impl_type::impl_type(const
boost::type_erasure::static_binding<Map>&) [with Map =
boost::mpl::map<boost::mpl::pair&lt;boost::type_erasure::_self, char [4]>,
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, mpl_::na>, Concept =
boost::mpl::vector<boost::type_erasure::copy_constructible&lt;>,
boost::type_erasure::typeid_<>, boost::type_erasure::ostreamable<> >]’
../boost/type_erasure/binding.hpp:94:35: instantiated from
‘boost::type_erasure::binding<Concept>::binding(const
boost::type_erasure::static_binding<Map>&) [with Map =
boost::mpl::map<boost::mpl::pair&lt;boost::type_erasure::_self, char [4]>,
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, mpl_::na>, Concept =
boost::mpl::vector<boost::type_erasure::copy_constructible&lt;>,
boost::type_erasure::typeid_<>, boost::type_erasure::ostreamable<> >]’
../boost/type_erasure/any.hpp:167:22: instantiated from
‘boost::type_erasure::any<Concept, T>::any(const U&) [with U = char [4],
Concept = boost::mpl::vector<boost::type_erasure::copy_constructible&lt;>,
boost::type_erasure::typeid_<>, boost::type_erasure::ostreamable<> >, T =
boost::type_erasure::_self]’
01.cpp:11:49: instantiated from ‘display::display(const T&) [with T =
char [4]]’
01.cpp:26:28: instantiated from here
../boost/type_erasure/detail/rebind_placeholders.hpp:161:64: error: function
returning an array
In file included from
../../../1_50_0_beta1.cygwin/boost/preprocessor/iteration/detail/iter/forward1.hpp:67:0,
                 from ../boost/type_erasure/detail/vtable.hpp:191,
                 from ../boost/type_erasure/binding.hpp:28,
                 from ../boost/type_erasure/any.hpp:39,
                 from 01.cpp:2:
../boost/type_erasure/detail/vtable.hpp: In instantiation of ‘const
boost::type_erasure::detail::vtable_storage4<boost::type_erasure::detail::vtable_adapter&lt;boost::type_erasure::constructible&lt;boost::type_erasure::_self(const
boost::type_erasure::_self&amp;)>,
boost::type_erasure::detail::storage(const
boost::type_erasure::detail::storage&)>,
boost::type_erasure::destructible<boost::type_erasure::_self>,
boost::type_erasure::typeid_<>,
boost::type_erasure::detail::vtable_adapter<boost::type_erasure::ostreamable&lt;>,
void(std::basic_ostream<char>&, const
boost::type_erasure::detail::storage&)> >
boost::type_erasure::detail::vtable_init4<boost::type_erasure::detail::vtable_storage4&lt;boost::type_erasure::detail::vtable_adapter&lt;boost::type_erasure::constructible&lt;boost::type_erasure::_self(const
boost::type_erasure::_self&amp;)>,
boost::type_erasure::detail::storage(const
boost::type_erasure::detail::storage&)>,
boost::type_erasure::destructible<boost::type_erasure::_self>,
boost::type_erasure::typeid_<>,
boost::type_erasure::detail::vtable_adapter<boost::type_erasure::ostreamable&lt;>,
void(std::basic_ostream<char>&, const
boost::type_erasure::detail::storage&)> >,
boost::type_erasure::detail::rebind_placeholders<boost::type_erasure::detail::vtable_adapter&lt;boost::type_erasure::constructible&lt;boost::type_erasure::_self(const
boost::type_erasure::_self&amp;)>,
boost::type_erasure::detail::storage(const
boost::type_erasure::detail::storage&)>,
boost::mpl::map<boost::mpl::pair&lt;boost::type_erasure::_self, char [4]>,
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, mpl_::na> >,
boost::type_erasure::destructible<char [4]>,
boost::type_erasure::typeid_<char [4]>,
boost::type_erasure::detail::vtable_adapter<boost::type_erasure::ostreamable&lt;std::basic_ostream&lt;char>,
char [4]>, void(std::basic_ostream<char>&, const
boost::type_erasure::detail::storage&)> >::value’:
../boost/type_erasure/binding.hpp:163:13: instantiated from
‘boost::type_erasure::binding<Concept>::impl_type::impl_type(const
boost::type_erasure::static_binding<Map>&) [with Map =
boost::mpl::map<boost::mpl::pair&lt;boost::type_erasure::_self, char [4]>,
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, mpl_::na>, Concept =
boost::mpl::vector<boost::type_erasure::copy_constructible&lt;>,
boost::type_erasure::typeid_<>, boost::type_erasure::ostreamable<> >]’
../boost/type_erasure/binding.hpp:94:35: instantiated from
‘boost::type_erasure::binding<Concept>::binding(const
boost::type_erasure::static_binding<Map>&) [with Map =
boost::mpl::map<boost::mpl::pair&lt;boost::type_erasure::_self, char [4]>,
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, mpl_::na>, Concept =
boost::mpl::vector<boost::type_erasure::copy_constructible&lt;>,
boost::type_erasure::typeid_<>, boost::type_erasure::ostreamable<> >]’
../boost/type_erasure/any.hpp:167:22: instantiated from
‘boost::type_erasure::any<Concept, T>::any(const U&) [with U = char [4],
Concept = boost::mpl::vector<boost::type_erasure::copy_constructible&lt;>,
boost::type_erasure::typeid_<>, boost::type_erasure::ostreamable<> >, T =
boost::type_erasure::_self]’
01.cpp:11:49: instantiated from ‘display::display(const T&) [with T =
char [4]]’
01.cpp:26:28: instantiated from here
../boost/type_erasure/detail/vtable.hpp:266:49: error: ‘value’ is not a
member of
‘boost::type_erasure::detail::rebind_placeholders<boost::type_erasure::detail::vtable_adapter&lt;boost::type_erasure::constructible&lt;boost::type_erasure::_self(const
boost::type_erasure::_self&amp;)>,
boost::type_erasure::detail::storage(const
boost::type_erasure::detail::storage&)>,
boost::mpl::map<boost::mpl::pair&lt;boost::type_erasure::_self, char [4]>,
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, mpl_::na> >’

Thanks,
--Lorenzo 

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