Re: [Boost-users] How to use the "type" member template pattern for using result_of?

28 Aug 2009


      Jesse Perla wrote:
...
Take the following function:
struct test_function
{
    template<typename Vector, typename IntType>
    typename Vector::value_type
    operator()(const Vector& x, IntType bound_value) const{
        return x[0] * x[0] + bound_value;
    }
};
I wasn't sure exactly how the "type" member template pattern works so 
that result_of will work.
I tried the following, but can't figure out how to extract the type of 
the arguments or convert to an MPL sequence?  Is there some trick I am 
missing?
struct test_function
{
template<typename Sig>
       struct result;

       template<typename This, typename Vector, typename IntType>
       struct result<This(Vector, IntType)>
       {
           typedef
               typename boost::remove_reference<
                   Vector
               >::type::value_type
           type;
       };
...
template<typename Vector, typename IntType>
    typename Vector::value_type //The type in the vector... can be a 
double or AD type
    operator()(const Vector& x, IntType bound_value) const{
        return x[0] * x[0] + bound_value;
    }
};
HTH,

-- 
Eric Niebler
BoostPro Computing
http://www.boostpro.com