Re: [Boost-users] [lambda] Can I use lambda::bind to a functor with a parametric return type?

Subject: Re: [Boost-users] [lambda] Can I use lambda::bind to a functor with a parametric return type?
From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2009-08-28 13:49:14

AMDG

Jesse Perla wrote:
> Thanks for the rapid response on the previous question.  Now for my real
> question:
>
> I am using an autodifferentiation library and want to use lambda's bind, but
> still return a generic type.  Is this possible?
>
> Here is the  function I wrote :
>
> struct test_function_impl
> {
>     //result_of supprt
>     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;
>     };
>
>
>     template<typename Vector, typename IntT>
>     typename Vector::value_type //The type in the vector... can be a double
> or AD type
>     operator()(const Vector& x, IntT y) const{
>         return x[0] * x[0] + y;
>     }
> };
>
>
> The function works on its own, and now std::tr1::result_of seems to work as
> well.
>
> However,   I cannot bind to this:
> using namespace boost::lambda;
>     ublas::bounded_vector<double, 1> x;
>     x[0] = 1.0;
>     int int_value = 1;
>
> //THIS FAILS!  Not sure if lambda's bind is using result_of?  Obviously,
> can't use the ret<> approach here.
>    auto f = bind(test_function_impl(), _1, int_value);
>
>
> Does lambda support this usage, or should I turn to Phoenix (if so, I am
> recognizing a trend here).
>   

Boost.Lambda uses its own protocol.

struct test_function_impl {
    template<class Args>
    struct sig {
        typedef typename boost::tuples::element<Args, 
1>::type::value_type type;
    };
};

In Christ,
Steven Watanabe