Re: [Boost-users] [fusion] How to use transform Metafunction?

From: Chris Weed (chrisweed_at_[hidden])
Date: 2007-03-16 12:15:41

On 3/16/07, Christian Henning <chhenning_at_[hidden]> wrote:
> Hi there, since there is no example in the docs and no test for it. I
> was wondering how to use fusion's transform metafunction.
>
> Here is what I want to do.
>
> template <typename T>
> struct add_vector
> {
>     typedef std::vector<T> type;
> };
>
> struct A;
> struct B;
> struct C;
>
> int main()
> {
>    typedef fusion::list< A, B, C > types;
>    typedef fusion::transform< types, add_vector<> >::type vector_of_types;
>
>    return 0;
> }
>
> The compiler is complaining that there are too few parameters for
> add_vector. In MPL you would just add _1 as the template parameter.
> But this doesn't work for fusion. So, how do I use it?
>

You need your function add_vector to be a Polymorphic function object.
I think you need something like this:

struct add_vector
{
  template <typename T>
  struct result
  {
    typedef std::vector<T> type;
  };
};

typedef typename boost::fusion::result_of::transform<types,
add_vector>::type tresult;

Chris