Re: [Boost-users] [fusion] named parameter technique with fusion::map

On 11/07/10 13:07, Alfredo Correa wrote: [snip]

template double derivative(double const& x){ ...already defined... }

double f(double x){return x*x;}

used as derivative<f>(1.);

the question is how to define a function "d" that takes a function like H with fusion container arguments, bind it against all arguments except one and calls derivative on that function. For example

d(1.,2.);

internally, the code should bind all the parameters except q to its corresponding values in the argument. in this case it is H binded with p=1. and then *derivative* of H( __, 2.) is called with argument 1.

[snip] What about just creating a fusion::vector for tuple containing an initial value, then store that into a templated functor taking the free variable index as one of the template arguments, and then the operator()(double value) would use value to set the tuple at the template index and then call the function. For example: //{-- free_at.hpp -- template < typename Tuple//e.g. fusion::vector < typename Functor//functor taking value of type Tuple. , unsigned FreeIndex//the index of the Tuple component that's "free"

struct free_at : Tuple { Functor functor ; template free_at(Functor f, Args... args) : Tuple(args...) , functor(f) {} template<unsigned FreeOther> free_at ( free_at < Tuple , Functor , FreeOther >const& free_other ) //Change the free_variable from FreeOther to FreeIndex : Tuple(free_other) , functor(free_other.f) {} template<typename FreeValu> typename Functor::result_type operator()(FreeValue free_value) { fusion::at_c<FreeIndex>(*this) = free_value; return functor(*this); } }: //}-- free_at.hpp -- Of course the above code uses variadic template notation, but I hope it's clear anyway. Also, Functor is assumed to take a Tuple as an argument. Obviously if the actual function used doesn't do that, then Functor could just contain a pointer to the actual function and expand the Tuple arguments in a call to the actual function. HTH. -Larry