C++ (Qt)
typedef type_list< double, int, std::string, float > list_of_types;
 
struct cals_sum : public any_visitor< double, list_of_types >
{
    double m_sum;
 
    cals_sum () : m_sum() {}
 
    double operator()( const std::string & str ) { return m_sum += std::stod(str); }
    template <class T>
    double operator()( const T & val ) { return m_sum += double( val ); }
};
 
 
struct to_string : public any_visitor< std::string, list_of_types >
{
    std::string operator()( const std::string & str ) const { return str; }
 
    template <class T>
    std::string operator()(const T & val) const { return std::to_string(val); }
};
 
int main()
{
    std::list< boost::any > many = {123, 3.14, 5.6f, std::string("2.71")};
 
    cals_sum visitor;
    for ( const auto & x : many )
        apply_any_visitor( visitor, x );
 
    std::cout << visitor.m_sum << std::endl;
    return 0;
}
 

C++ (Qt)
template <class Visitor, class TypeList>
struct any_cast_helper
{
    static typename Visitor::result_type get(const boost::any & any, Visitor & visitor)
    {
        if (any.type() == typeid(typename TypeList::first_type))
            return visitor(boost::any_cast<typename TypeList::first_type >(any));
 
        return any_cast_helper<Visitor, typename TypeList::next_type_list>::get(any, visitor);
    }
    static typename Visitor::result_type get(const boost::any & any, const Visitor & visitor)
    {
        if (any.type() == typeid(typename TypeList::first_type))
            return visitor(boost::any_cast<typename TypeList::first_type>(any));
 
        return any_cast_helper<Visitor, typename TypeList::next_type_list>::get(any, visitor);
    }
};
 
 
template <class Visitor>
struct any_cast_helper<Visitor, null_type>
{
    static typename Visitor::result_type get(const boost::any &, Visitor &) throw(std::bad_cast)
    {
        throw std::bad_cast();
    }
    static typename Visitor::result_type get(const boost::any &, const Visitor &) throw(std::bad_cast)
    {
        throw std::bad_cast();
    }
};
 
 
template <class Visitor>
typename Visitor::result_type apply_any_visitor(const Visitor & visitor, const boost::any & any)
{
    return any_cast_helper<Visitor, typename Visitor::type_list>::get(any, visitor);
}
 
template <class Visitor>
typename Visitor::result_type apply_any_visitor( Visitor & visitor, const boost::any & any)
{
    return any_cast_helper<Visitor, typename Visitor::type_list>::get(any, visitor);
}
 

C++ (Qt)
 
struct AbstractAnyFabric
{
    virtual ~AbstractAnyFabric () {}
    virtual boost::any make () = 0;
};
 
template < typename _Type >
struct AnyFabric : public AbstractAnyFabric
{
    virtual boost::any make ()
    {
        return boost::any( _Type() );
    }
};
 

template < typename _Type >
const AbstractAnyFactory & any_factory ()
{
    static const AnyFactory< _Type > factory;
    return factory;
}

C++ (Qt)
Result foo ( const boost::any & )
 

C++ (Qt)
type_list<double, int, float,  std::string>
 

C++ (Qt)
template < typename _Type >
struct to_double_helper;
 
template <>
struct to_double_helper< double >
{
    static double execute ( const boost::any & value )
    {
        return boost::any_cast< double >( value );
    }
};
 
template <>
struct to_double_helper< std::string >
{
    static double execute ( const boost::any & value )
    {
        return std::stod( boost::any_cast< std::string >( value ) );
    }
};
 
double to_double ( const boost::any & value )
{
    if ( value.type() == typeid( double ) )
        return to_double_helper< double >::execute( value );
    if ( value.type() == typeid( std::string ) )
        return to_double_helper< std::string >::execute( value );
    //...
 
 
    return 0;
}
 
int main()
{
    std::list< boost::any > many = {123, 3.14, 5.6f, std::string("2.71")};
    double sum = 0.0;
 
    for ( const auto & x : many )
        sum += to_double( x );
 
    std::cout << sum << std::endl;
    return 0;
}
 

C++ (Qt)
typedef double ( *to_double_function )( const boost::any & );
 
to_double_function to_double_function_for_type ( const std::type_info & type )
{
    to_double_function result = to_double_function();
    //...
    return result;
}
 
double to_double ( const boost::any & value )
{
    return (*to_double_function_for_type( value.type() ) )( value );
}