Re: [Boost-users] [fusion] const and transform algorithm

vicente.botet wrote:

Hi,

What is the reason fusion::transform taskes a const Sequence? template< typename Sequence, typename F > typename result_of::transform::type transform( Sequence const& seq, F f);

Does this means that the transform do not change the sequence itself o also its elements?

Yes. Fusion transform returns a lazy (transform) view. This view is non-mutating. It is not like STL's transform which mutates the target container in place. Fusion's is purely functional and lazily evaluated.

Why the following do not compiles struct get { template<typename Sig> struct result; template<typename T> struct result { typedef typename boost::remove_reference<T>::type ACT; typedef typename ACT::result_type type; }; template<typename ACT> typename ACT::result_type operator()(ACT& act) const { return act.get(); } }; boost::tuple t; boost::fusion::result_of::transform< boost::tuple , get>::type res= boost::fusion::transform(t, get());

transform call to get()(const shared_future<int>&act). How can I make a transformation changing also the sequence itself?

The result of transform is a transform_view, so the function get is not really called. How can I assign this to a boost::tuple = ??(boost::fusion::transform(t, get())); boost::as_vector? Is there a as_tuple function? Should this force the evaluation of the get function?

As I said, Fusion transform is purely functional. The result of a transform is a view. The function will only be called when you iterate over the view. The transformation does not change/mutate the sequence itself. If that's what you want, you can assign the view back to the original container. For example: vector v; v = transform(v, f); Regards, -- Joel de Guzman http://www.boostpro.com http://spirit.sf.net