Hi there, is it possible to have a stateful functor object when using
fusion::for_each() loop.
I would like to to the following:
#include <vector>
#include
#include
#include
#include
#include
#include
#include
#include
#include
using namespace std;
using namespace boost;
struct A { void print() { cout << "A" << endl; }};
struct B { void print() { cout << "B" << endl; }};
struct C { void print() { cout << "C" << endl; }};
std::vector<A> find_all( A ) { return std::vector<A>(12); }
std::vector<B> find_all( B ) { return std::vector<B>(12); }
std::vector<C> find_all( C ) { return std::vector<C>(12); }
typedef mpl::list< A, B, C > _types_;
template <typename T>
struct add_vector
{
typedef std::vector<T> type;
};
struct find_all_
{
template< class T >
void operator()( T& t ) const
{
typedef typename T::value_type type;
type v;
t = find_all( v );
}
};
struct check_size
{
check_size()
: _init( false ), _size( 0 ) {}
template< class T >
void operator()( T& t )
{
if( !_init )
{
_size = t.size();
_init = true;
return;
}
if( _size != t.size() )
{
throw runtime_error( "vectors don't match up." );
}
}
private:
bool _init;
size_t _size;
};
struct print
{
template< class T >
void operator()( T& vec ) const
{
vec[0].print();
}
};
int main()
{
typedef mpl::transform1< _types_, add_vector >::type
_mpl_list_of_vectors_;
typedef fusion::result_of::as_list<_mpl_list_of_vectors_>::type
_fusion_list_of_vectors_;
_fusion_list_of_vectors_ vectors;
fusion::for_each( vectors, find_all_() );
fusion::for_each( vectors, check_size() );
return 0;
}
Unfortunately it wont compile. The error messages are:
c:\boost\boost\fusion\algorithm\iteration\detail\for_each.hpp(28) :
error C3848: expression having type 'const check_size' would lose some
const-volatile qualifiers in order to call 'void check_size::operator
()<T>(T &)'
with
[
T=boost::fusion::extension::deref_impl::apply>::value_type
]
c:\boost\boost\fusion\algorithm\iteration\for_each.hpp(37) :
see reference to function template instantiation 'void
boost::fusion::detail::for_each::apply<Sequence>::type,boost::fusion::extension::end_impl::apply<Sequence>::type,F>(const
First &,const Last &,const F &,boost::mpl::false_)' being compiled
with
[
Sequence=_fusion_list_of_vectors_,
F=check_size,
First=boost::fusion::extension::begin_impl::apply<_fusion_list_of_vectors_>::type,
Last=boost::fusion::extension::end_impl::apply<_fusion_list_of_vectors_>::type
]
test.cpp(100) : see reference to function template
instantiation 'void
boost::fusion::for_each<_fusion_list_of_vectors_,check_size>(Sequence
&,const F &)' being compiled
with
[
Sequence=_fusion_list_of_vectors_,
F=check_size
]
Any ideas?
Christian
