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

Subject: Re: [Boost-users] How to use the "type" member template pattern for using result_of?
From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2009-08-28 12:47:00

AMDG

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 Args>
>     struct result {
>        //HOW TO CONVERT TO MPL SEQUENCE OR ANOTHER APPROACH?
>         typedef typename boost::mpl::at_c<Args, 0 >::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;
>     }
> };
>   

struct test_function {
    template<typename Sig>
    struct result;
    template<typename This, typename Arg1, typename Arg2>
    struct result<This(Arg1, Arg2)> {
        typedef typename boost::remove_reference<Arg1>::type::value_type 
type;
    };
};

In Christ,
Steven Watanabe